//高大上
看到一篇相关的好文章,引用下:http://www.cnblogs.com/leoo2sk/archive/2011/07/10/mysql-index.html 。相当滴不错,备忘下。
在这篇文章中http://blog.csdn.net/weege/article/details/6526512介绍了B-tree/B+tree/B*tree,并且介绍了B-tree的查找,插入,删除操作。现在重新认识下B-TREE(温故而知新嘛~,确实如此。自己在写代码中会体会到,B-tree的操作出现的条件相对其他树比较复杂,调试也是一个理通思路的过程。)
B-tree又叫平衡多路查找树。一棵m阶的B-tree (m叉树)的特性如下:
(其中ceil(x)是一个取上限的函数)
1) 树中每个结点至多有m个孩子;
2) 除根结点和叶子结点外,其它每个结点至少有有ceil(m / 2)个孩子;
3) 若根结点不是叶子结点,则至少有2个孩子(特殊情况:没有孩子的根结点,即根结点为叶子结点,整棵树只有一个根节点);
4) 所有叶子结点都出现在同一层,叶子结点不包含任何关键字信息(可以看做是外部结点或查询失败的结点,实际上这些结点不存在,指向这些结点的指针都为null)(PS:这种说法是按照严蔚敏那本教材给出的,具体操作不同而定,下面的实现中的叶子结点是树的终端结点,即没有孩子的结点);
5) 每个非终端结点中包含有n个关键字信息: (n,P0,K1,P1,K2,P2,......,Kn,Pn)。其中:
a) Ki (i=1...n)为关键字,且关键字按顺序排序K(i-1)< Ki。
b) Pi为指向子树根的接点,且指针P(i-1)指向子树种所有结点的关键字均小于Ki,但都大于K(i-1)。
c) 关键字的个数n必须满足: ceil(m / 2)-1 <= n <= m-1。
具体代码实现如下:(这里只是给出了简单的B-Tree结构,在内存中的数据操作。具体详情见代码吧~!)
头文件:(提供B-Tree基本的操作接口)
- /***************************************************************************
- @coder:weedge E-mail:weege@126.com
- @date:2011/08/27
- @comment:
- 参考:http://www.cppblog.com/converse/archive/2009/10/13/98521.html
- 实现对order序(阶)的B-TREE结构基本操作的封装。
- 查找:search,插入:insert,删除:remove。
- 创建:create,销毁:destory,打印:print。
- **********************************************************/
- #ifndef BTREE_H
- #define BTREE_H
- #ifdef __cplusplus
- extern "C" {
- #endif
- ////* 定义m序(阶)B 树的最小度数BTree_D=ceil(m/2)*/
- /// 在这里定义每个节点中关键字的最大数目为:2 * BTree_D - 1,即序(阶):2 * BTree_D.
- #define BTree_D 2
- #define ORDER (BTree_D * 2) //定义为4阶B-tree,2-3-4树。(偶序)
- //#define ORDER (BTree_D * 2-1)//最简单为3阶B-tree,2-3树。(奇序)
- typedef int KeyType;
- typedef struct BTNode{
- int keynum; /// 结点中关键字的个数,ceil(ORDER/2)-1<= keynum <= ORDER-1
- KeyType key[ORDER-1]; /// 关键字向量为key[0..keynum - 1]
- struct BTNode* child[ORDER]; /// 孩子指针向量为child[0..keynum]
- char isLeaf; /// 是否是叶子节点的标志
- }BTNode;
- typedef BTNode* BTree; ///定义BTree
- ///给定数据集data,创建BTree。
- void BTree_create(BTree* tree, const KeyType* data, int length);
- ///销毁BTree,释放内存空间。
- void BTree_destroy(BTree* tree);
- ///在BTree中插入关键字key。
- void BTree_insert(BTree* tree, KeyType key);
- ///在BTree中移除关键字key。
- void BTree_remove(BTree* tree, KeyType key);
- ///深度遍历BTree打印各层结点信息。
- void BTree_print(const BTree tree, int layer);
- /// 在BTree中查找关键字 key,
- /// 成功时返回找到的节点的地址及 key 在其中的位置 *pos
- /// 失败时返回 NULL 及查找失败时扫描到的节点位置 *pos
- BTNode* BTree_search(const BTree tree, int key, int* pos);
- #ifdef __cplusplus
- }
- #endif
- #endif
源文件:(提供B-Tree基本的基本操作的实现)
- /***************************************************************************
- @coder:weedge E-mail:weege@126.com
- @date:2011/08/27
- @comment:
- 参考:http://www.cppblog.com/converse/archive/2009/10/13/98521.html
- 实现对order序(阶)的B-TREE结构基本操作的封装。
- 查找:search,插入:insert,删除:remove。
- 创建:create,销毁:destory,打印:print。
- **********************************************************/
- #include <stdlib.h>
- #include <stdio.h>
- #include <assert.h>
- #include "btree.h"
- //#define max(a, b) (((a) > (b)) ? (a) : (b))
- #define cmp(a, b) ( ( ((a)-(b)) >= (0) ) ? (1) : (0) ) //比较a,b大小
- #define DEBUG_BTREE
- // 模拟向磁盘写入节点
- void disk_write(BTNode* node)
- {
- int i;
- //打印出结点中的全部元素,方便调试查看keynum之后的元素是否为0(即是否存在垃圾数据);而不是keynum个元素。
- printf("向磁盘写入节点");
- for(i=0;i<ORDER-1;i++){
- printf("%c",node->key[i]);
- }
- printf("\n");
- }
- // 模拟从磁盘读取节点
- void disk_read(BTNode** node)
- {
- int i;
- //打印出结点中的全部元素,方便调试查看keynum之后的元素是否为0(即是否存在垃圾数据);而不是keynum个元素。
- printf("向磁盘读取节点");
- for(i=0;i<ORDER-1;i++){
- printf("%c",(*node)->key[i]);
- }
- printf("\n");
- }
- // 按层次打印 B 树
- void BTree_print(const BTree tree, int layer)
- {
- int i;
- BTNode* node = tree;
- if (node) {
- printf("第 %d 层, %d node : ", layer, node->keynum);
- //打印出结点中的全部元素,方便调试查看keynum之后的元素是否为0(即是否存在垃圾数据);而不是keynum个元素。
- for (i = 0; i < ORDER-1; ++i) {
- //for (i = 0; i < node->keynum; ++i) {
- printf("%c ", node->key[i]);
- }
- printf("\n");
- ++layer;
- for (i = 0 ; i <= node->keynum; i++) {
- if (node->child[i]) {
- BTree_print(node->child[i], layer);
- }
- }
- }
- else {
- printf("树为空。\n");
- }
- }
- // 结点node内对关键字进行二分查找。
- int binarySearch(BTNode* node, int low, int high, KeyType Fkey)
- {
- int mid;
- while (low<=high)
- {
- mid = low + (high-low)/2;
- if (Fkey<node->key[mid])
- {
- high = mid-1;
- }
- if (Fkey>node->key[mid])
- {
- low = mid+1;
- }
- if (Fkey==node->key[mid])
- {
- return mid;//返回下标。
- }
- }
- return -1;//未找到返回-1.
- }
- //=======================================================insert=====================================
- /***************************************************************************************
- 将分裂的结点中的一半元素给新建的结点,并且将分裂结点中的中间关键字元素上移至父节点中。
- parent 是一个非满的父节点
- node 是 tree 孩子表中下标为 index 的孩子节点,且是满的,需分裂。
- *******************************************************************/
- void BTree_split_child(BTNode* parent, int index, BTNode* node)
- {
- int i;
- BTNode* newNode;
- #ifdef DEBUG_BTREE
- printf("BTree_split_child!\n");
- #endif
- assert(parent && node);
- // 创建新节点,存储 node 中后半部分的数据
- newNode = (BTNode*)calloc(sizeof(BTNode), 1);
- if (!newNode) {
- printf("Error! out of memory!\n");
- return;
- }
- newNode->isLeaf = node->isLeaf;
- newNode->keynum = BTree_D - 1;
- // 拷贝 node 后半部分关键字,然后将node后半部分置为0。
- for (i = 0; i < newNode->keynum; ++i){
- newNode->key[i] = node->key[BTree_D + i];
- node->key[BTree_D + i] = 0;
- }
- // 如果 node 不是叶子节点,拷贝 node 后半部分的指向孩子节点的指针,然后将node后半部分指向孩子节点的指针置为NULL。
- if (!node->isLeaf) {
- for (i = 0; i < BTree_D; i++) {
- newNode->child[i] = node->child[BTree_D + i];
- node->child[BTree_D + i] = NULL;
- }
- }
- // 将 node 分裂出 newNode 之后,里面的数据减半
- node->keynum = BTree_D - 1;
- // 调整父节点中的指向孩子的指针和关键字元素。分裂时父节点增加指向孩子的指针和关键元素。
- for (i = parent->keynum; i > index; --i) {
- parent->child[i + 1] = parent->child[i];
- }
- parent->child[index + 1] = newNode;
- for (i = parent->keynum - 1; i >= index; --i) {
- parent->key[i + 1] = parent->key[i];
- }
- parent->key[index] = node->key[BTree_D - 1];
- ++parent->keynum;
- node->key[BTree_D - 1] = 0;
- // 写入磁盘
- disk_write(parent);
- disk_write(newNode);
- disk_write(node);
- }
- void BTree_insert_nonfull(BTNode* node, KeyType key)
- {
- int i;
- assert(node);
- // 节点是叶子节点,直接插入
- if (node->isLeaf) {
- i = node->keynum - 1;
- while (i >= 0 && key < node->key[i]) {
- node->key[i + 1] = node->key[i];
- --i;
- }
- node->key[i + 1] = key;
- ++node->keynum;
- // 写入磁盘
- disk_write(node);
- }
- // 节点是内部节点
- else {
- /* 查找插入的位置*/
- i = node->keynum - 1;
- while (i >= 0 && key < node->key[i]) {
- --i;
- }
- ++i;
- // 从磁盘读取孩子节点
- disk_read(&node->child[i]);
- // 如果该孩子节点已满,分裂调整值
- if (node->child[i]->keynum == (ORDER-1)) {
- BTree_split_child(node, i, node->child[i]);
- // 如果待插入的关键字大于该分裂结点中上移到父节点的关键字,在该关键字的右孩子结点中进行插入操作。
- if (key > node->key[i]) {
- ++i;
- }
- }
- BTree_insert_nonfull(node->child[i], key);
- }
- }
- void BTree_insert(BTree* tree, KeyType key)
- {
- BTNode* node;
- BTNode* root = *tree;
- #ifdef DEBUG_BTREE
- printf("BTree_insert:\n");
- #endif
- // 树为空
- if (NULL == root) {
- root = (BTNode*)calloc(sizeof(BTNode), 1);
- if (!root) {
- printf("Error! out of memory!\n");
- return;
- }
- root->isLeaf = 1;
- root->keynum = 1;
- root->key[0] = key;
- *tree = root;
- // 写入磁盘
- disk_write(root);
- return;
- }
- // 根节点已满,插入前需要进行分裂调整
- if (root->keynum == (ORDER-1)) {
- // 产生新节点当作根
- node = (BTNode*)calloc(sizeof(BTNode), 1);
- if (!node) {
- printf("Error! out of memory!\n");
- return;
- }
- *tree = node;
- node->isLeaf = 0;
- node->keynum = 0;
- node->child[0] = root;
- BTree_split_child(node, 0, root);
- BTree_insert_nonfull(node, key);
- }
- // 根节点未满,在当前节点中插入 key
- else {
- BTree_insert_nonfull(root, key);
- }
- }
- //=================================================remove========================================
- /***********************************************************************************
- // 对 tree 中的节点 node 进行合并孩子节点处理.
- // 注意:孩子节点的 keynum 必须均已达到下限,即均等于 BTree_D - 1
- // 将 tree 中索引为 index 的 key 下移至左孩子结点中,
- // 将 node 中索引为 index + 1 的孩子节点合并到索引为 index 的孩子节点中,右孩子合并到左孩子结点中。
- // 并调相关的 key 和指针。
- ***************************************************/
- void BTree_merge_child(BTree* tree, BTNode* node, int index)
- {
- int i;
- KeyType key;
- BTNode *leftChild, *rightChild;
- #ifdef DEBUG_BTREE
- printf("BTree_merge_child!\n");
- #endif
- assert(tree && node && index >= 0 && index < node->keynum);
- key = node->key[index];
- leftChild = node->child[index];
- rightChild = node->child[index + 1];
- assert(leftChild && leftChild->keynum == BTree_D - 1
- && rightChild && rightChild->keynum == BTree_D - 1);
- // 将 node中关键字下标为index 的 key 下移至左孩子结点中,该key所对应的右孩子结点指向node的右孩子结点中的第一个孩子。
- leftChild->key[leftChild->keynum] = key;
- leftChild->child[leftChild->keynum + 1] = rightChild->child[0];
- ++leftChild->keynum;
- // 右孩子的元素合并到左孩子结点中。
- for (i = 0; i < rightChild->keynum; ++i) {
- leftChild->key[leftChild->keynum] = rightChild->key[i];
- leftChild->child[leftChild->keynum + 1] = rightChild->child[i + 1];
- ++leftChild->keynum;
- }
- // 在 node 中下移的 key后面的元素前移
- for (i = index; i < node->keynum - 1; ++i) {
- node->key[i] = node->key[i + 1];
- node->child[i + 1] = node->child[i + 2];
- }
- node->key[node->keynum - 1] = 0;
- node->child[node->keynum] = NULL;
- --node->keynum;
- // 如果根节点没有 key 了,并将根节点调整为合并后的左孩子节点;然后删除释放空间。
- if (node->keynum == 0) {
- if (*tree == node) {
- *tree = leftChild;
- }
- free(node);
- node = NULL;
- }
- free(rightChild);
- rightChild = NULL;
- }
- void BTree_recursive_remove(BTree* tree, KeyType key)
- {
- // B-数的保持条件之一:
- // 非根节点的内部节点的关键字数目不能少于 BTree_D - 1
- int i, j, index;
- BTNode *root = *tree;
- BTNode *node = root;
- if (!root) {
- printf("Failed to remove %c, it is not in the tree!\n", key);
- return;
- }
- // 结点中找key。
- index = 0;
- while (index < node->keynum && key > node->key[index]) {
- ++index;
- }
- /*======================含有key的当前结点时的情况====================
- node:
- index of Key: i-1 i i+1
- +---+---+---+---+
- * key *
- +---+---+---+---+---+
- / \
- index of Child: i i+1
- / \
- +---+---+ +---+---+
- * * * *
- +---+---+---+ +---+---+---+
- leftChild rightChild
- ============================================================*/
- /*一、结点中找到了关键字key的情况.*/
- if (index < node->keynum && node->key[index] == key) {
- BTNode *leftChild, *rightChild;
- KeyType leftKey, rightKey;
- /* 1,所在节点是叶子节点,直接删除*/
- if (node->isLeaf) {
- for (i = index; i < node->keynum-1; ++i) {
- node->key[i] = node->key[i + 1];
- //node->child[i + 1] = node->child[i + 2];叶子节点的孩子结点为空,无需移动处理。
- }
- node->key[node->keynum-1] = 0;
- //node->child[node->keynum] = NULL;
- --node->keynum;
- if (node->keynum == 0) {
- assert(node == *tree);
- free(node);
- *tree = NULL;
- }
- return;
- }
- /*2.选择脱贫致富的孩子结点。*/
- // 2a,选择相对富有的左孩子结点。
- // 如果位于 key 前的左孩子结点的 key 数目 >= BTree_D,
- // 在其中找 key 的左孩子结点的最后一个元素上移至父节点key的位置。
- // 然后在左孩子节点中递归删除元素leftKey。
- else if (node->child[index]->keynum >= BTree_D) {
- leftChild = node->child[index];
- leftKey = leftChild->key[leftChild->keynum - 1];
- node->key[index] = leftKey;
- BTree_recursive_remove(&leftChild, leftKey);
- }
- // 2b,选择相对富有的右孩子结点。
- // 如果位于 key 后的右孩子结点的 key 数目 >= BTree_D,
- // 在其中找 key 的右孩子结点的第一个元素上移至父节点key的位置
- // 然后在右孩子节点中递归删除元素rightKey。
- else if (node->child[index + 1]->keynum >= BTree_D) {
- rightChild = node->child[index + 1];
- rightKey = rightChild->key[0];
- node->key[index] = rightKey;
- BTree_recursive_remove(&rightChild, rightKey);
- }
- /*左右孩子结点都刚脱贫。删除前需要孩子结点的合并操作*/
- // 2c,左右孩子结点只包含 BTree_D - 1 个节点,
- // 合并是将 key 下移至左孩子节点,并将右孩子节点合并到左孩子节点中,
- // 删除右孩子节点,在父节点node中移除 key 和指向右孩子节点的指针,
- // 然后在合并了的左孩子节点中递归删除元素key。
- else if (node->child[index]->keynum == BTree_D - 1
- && node->child[index + 1]->keynum == BTree_D - 1){
- leftChild = node->child[index];
- BTree_merge_child(tree, node, index);
- // 在合并了的左孩子节点中递归删除 key
- BTree_recursive_remove(&leftChild, key);
- }
- }
- /*======================未含有key的当前结点时的情况====================
- node:
- index of Key: i-1 i i+1
- +---+---+---+---+
- * keyi *
- +---+---+---+---+---+
- / | \
- index of Child: i-1 i i+1
- / | \
- +---+---+ +---+---+ +---+---+
- * * * * * *
- +---+---+---+ +---+---+---+ +---+---+---+
- leftSibling Child rightSibling
- ============================================================*/
- /*二、结点中未找到了关键字key的情况.*/
- else {
- BTNode *leftSibling, *rightSibling, *child;
- // 3. key 不在内节点 node 中,则应当在某个包含 key 的子节点中。
- // key < node->key[index], 所以 key 应当在孩子节点 node->child[index] 中
- child = node->child[index];
- if (!child) {
- printf("Failed to remove %c, it is not in the tree!\n", key);
- return;
- }
- /*所需查找的该孩子结点刚脱贫的情况*/
- if (child->keynum == BTree_D - 1) {
- leftSibling = NULL;
- rightSibling = NULL;
- if (index - 1 >= 0) {
- leftSibling = node->child[index - 1];
- }
- if (index + 1 <= node->keynum) {
- rightSibling = node->child[index + 1];
- }
- /*选择致富的相邻兄弟结点。*/
- // 3a,如果所在孩子节点相邻的兄弟节点中有节点至少包含 BTree_D 个关键字
- // 将 node 的一个关键字key[index]下移到 child 中,将相对富有的相邻兄弟节点中一个关键字上移到
- // node 中,然后在 child 孩子节点中递归删除 key。
- if ((leftSibling && leftSibling->keynum >= BTree_D)
- || (rightSibling && rightSibling->keynum >= BTree_D)) {
- int richR = 0;
- if(rightSibling) richR = 1;
- if(leftSibling && rightSibling) {
- richR = cmp(rightSibling->keynum,leftSibling->keynum);
- }
- if (rightSibling && rightSibling->keynum >= BTree_D && richR) {
- //相邻右兄弟相对富有,则该孩子先向父节点借一个元素,右兄弟中的第一个元素上移至父节点所借位置,并进行相应调整。
- child->key[child->keynum] = node->key[index];
- child->child[child->keynum + 1] = rightSibling->child[0];
- ++child->keynum;
- node->key[index] = rightSibling->key[0];
- for (j = 0; j < rightSibling->keynum - 1; ++j) {//元素前移
- rightSibling->key[j] = rightSibling->key[j + 1];
- rightSibling->child[j] = rightSibling->child[j + 1];
- }
- rightSibling->key[rightSibling->keynum-1] = 0;
- rightSibling->child[rightSibling->keynum-1] = rightSibling->child[rightSibling->keynum];
- rightSibling->child[rightSibling->keynum] = NULL;
- --rightSibling->keynum;
- }
- else {//相邻左兄弟相对富有,则该孩子向父节点借一个元素,左兄弟中的最后元素上移至父节点所借位置,并进行相应调整。
- for (j = child->keynum; j > 0; --j) {//元素后移
- child->key[j] = child->key[j - 1];
- child->child[j + 1] = child->child[j];
- }
- child->child[1] = child->child[0];
- child->child[0] = leftSibling->child[leftSibling->keynum];
- child->key[0] = node->key[index - 1];
- ++child->keynum;
- node->key[index - 1] = leftSibling->key[leftSibling->keynum - 1];
- leftSibling->key[leftSibling->keynum - 1] = 0;
- leftSibling->child[leftSibling->keynum] = NULL;
- --leftSibling->keynum;
- }
- }
- /*相邻兄弟结点都刚脱贫。删除前需要兄弟结点的合并操作,*/
- // 3b, 如果所在孩子节点相邻的兄弟节点都只包含 BTree_D - 1 个关键字,
- // 将 child 与其一相邻节点合并,并将 node 中的一个关键字下降到合并节点中,
- // 再在 node 中删除那个关键字和相关指针,若 node 的 key 为空,删之,并调整根为合并结点。
- // 最后,在相关孩子节点child中递归删除 key。
- else if ((!leftSibling || (leftSibling && leftSibling->keynum == BTree_D - 1))
- && (!rightSibling || (rightSibling && rightSibling->keynum == BTree_D - 1))) {
- if (leftSibling && leftSibling->keynum == BTree_D - 1) {
- BTree_merge_child(tree, node, index - 1);//node中的右孩子元素合并到左孩子中。
- child = leftSibling;
- }
- else if (rightSibling && rightSibling->keynum == BTree_D - 1) {
- BTree_merge_child(tree, node, index);//node中的右孩子元素合并到左孩子中。
- }
- }
- }
- BTree_recursive_remove(&child, key);//调整后,在key所在孩子结点中继续递归删除key。
- }
- }
- void BTree_remove(BTree* tree, KeyType key)
- {
- #ifdef DEBUG_BTREE
- printf("BTree_remove:\n");
- #endif
- if (*tree==NULL)
- {
- printf("BTree is NULL!\n");
- return;
- }
- BTree_recursive_remove(tree, key);
- }
- //=====================================search====================================
- BTNode* BTree_recursive_search(const BTree tree, KeyType key, int* pos)
- {
- int i = 0;
- while (i < tree->keynum && key > tree->key[i]) {
- ++i;
- }
- // Find the key.
- if (i < tree->keynum && tree->key[i] == key) {
- *pos = i;
- return tree;
- }
- // tree 为叶子节点,找不到 key,查找失败返回
- if (tree->isLeaf) {
- return NULL;
- }
- // 节点内查找失败,但 tree->key[i - 1]< key < tree->key[i],
- // 下一个查找的结点应为 child[i]
- // 从磁盘读取第 i 个孩子的数据
- disk_read(&tree->child[i]);
- // 递归地继续查找于树 tree->child[i]
- return BTree_recursive_search(tree->child[i], key, pos);
- }
- BTNode* BTree_search(const BTree tree, KeyType key, int* pos)
- {
- #ifdef DEBUG_BTREE
- printf("BTree_search:\n");
- #endif
- if (!tree) {
- printf("BTree is NULL!\n");
- return NULL;
- }
- *pos = -1;
- return BTree_recursive_search(tree,key,pos);
- }
- //===============================create===============================
- void BTree_create(BTree* tree, const KeyType* data, int length)
- {
- int i, pos = -1;
- assert(tree);
- #ifdef DEBUG_BTREE
- printf("\n 开始创建 B-树,关键字为:\n");
- for (i = 0; i < length; i++) {
- printf(" %c ", data[i]);
- }
- printf("\n");
- #endif
- for (i = 0; i < length; i++) {
- #ifdef DEBUG_BTREE
- printf("\n插入关键字 %c:\n", data[i]);
- #endif
- BTree_search(*tree,data[i],&pos);//树的递归搜索。
- if (pos!=-1)
- {
- printf("this key %c is in the B-tree,not to insert.\n",data[i]);
- }else{
- BTree_insert(tree, data[i]);//插入元素到BTree中。
- }
- #ifdef DEBUG_BTREE
- BTree_print(*tree,1);//树的深度遍历,从第一层开始。
- #endif
- }
- printf("\n");
- }
- //===============================destroy===============================
- void BTree_destroy(BTree* tree)
- {
- int i;
- BTNode* node = *tree;
- if (node) {
- for (i = 0; i <= node->keynum; i++) {
- BTree_destroy(&node->child[i]);
- }
- free(node);
- }
- *tree = NULL;
- }
测试文件:(测试B-Tree基本的操作接口)
- /***************************************************************************
- @coder:weedge E-mail:weege@126.com
- @date:2011/08/28
- @comment:
- 测试order序(阶)的B-TREE结构基本操作。
- 查找:search,插入:insert,删除:remove。
- 创建:create,销毁:destory,打印:print。
- **********************************************************/
- #include <stdio.h>
- #include "btree.h"
- void test_BTree_search(BTree tree, KeyType key)
- {
- int pos = -1;
- BTNode* node = BTree_search(tree, key, &pos);
- if (node) {
- printf("在%s节点(包含 %d 个关键字)中找到关键字 %c,其索引为 %d\n",
- node->isLeaf ? "叶子" : "非叶子",
- node->keynum, key, pos);
- }
- else {
- printf("在树中找不到关键字 %c\n", key);
- }
- }
- void test_BTree_remove(BTree* tree, KeyType key)
- {
- printf("\n移除关键字 %c \n", key);
- BTree_remove(tree, key);
- BTree_print(*tree);
- printf("\n");
- }
- void test_btree()
- {
- KeyType array[] = {
- 'G','G', 'M', 'P', 'X', 'A', 'C', 'D', 'E', 'J', 'K',
- 'N', 'O', 'R', 'S', 'T', 'U', 'V', 'Y', 'Z', 'F', 'X'
- };
- const int length = sizeof(array)/sizeof(KeyType);
- BTree tree = NULL;
- BTNode* node = NULL;
- int pos = -1;
- KeyType key1 = 'R'; // in the tree.
- KeyType key2 = 'B'; // not in the tree.
- // 创建
- BTree_create(&tree, array, length);
- printf("\n=== 创建 B- 树 ===\n");
- BTree_print(tree);
- printf("\n");
- // 查找
- test_BTree_search(tree, key1);
- printf("\n");
- test_BTree_search(tree, key2);
- // 移除不在B树中的元素
- test_BTree_remove(&tree, key2);
- printf("\n");
- // 插入关键字
- printf("\n插入关键字 %c \n", key2);
- BTree_insert(&tree, key2);
- BTree_print(tree);
- printf("\n");
- test_BTree_search(tree, key2);
- // 移除关键字
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'M';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'E';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'G';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'A';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'D';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'K';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'P';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'J';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'C';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'X';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'O';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'V';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'R';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'U';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'T';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'N';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'S';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'Y';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'F';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- key2 = 'Z';
- test_BTree_remove(&tree, key2);
- test_BTree_search(tree, key2);
- // 销毁
- BTree_destroy(&tree);
- }
- int main()
- {
- test_btree();
- return 0;
- }
另外参考《Data.structures.and.Program.Design.in.Cpp》-Section 11.3:EXTERNALSEARCHING:B-TREES的讲解实现,这边书个人认为比较经典,如果对数据结构和算法比较感兴趣的话,可以作为参考读物,不错的,根据数据结构上的操作与程序上的实现相结合,讲的很细。这本书好像没有中文版的,即使有,也推荐看原版吧,毕竟写代码都是用英文字符,实现也比较贴切易懂。去网上找这本书的资料还挺多的。而且国内有些大学也参考这本书讲解数据结构和算法。比如:http://sist.sysu.edu.cn/~isslxm/DSA/CS09/。
头文件:(采用C++模板(template)来实现B-Tree基本的操作接口)
- /***************************************************************************
- @editer:weedge E-mail:weege@126.com
- @date:2011/08/27
- @comment:
- Data.structures.and.Program.Design.in.Cpp
- Section 11.3:EXTERNALSEARCHING:B-TREES
- 采用泛型编程(模板template),Record为关键字类型,order为序(阶),
- 实现对order序(阶)的B-TREE结构基本操作的封装。
- 查找:search,插入:insert,删除:remove。
- **********************************************************/
- #ifndef B_Tree_H_
- #define B_Tree_H_
- enum Error_code{overflow=-2,duplicate_error=-1,not_present=0,success=1};
- template <class Record, int order>
- struct B_node {
- /// data members:
- int count;
- Record data[order - 1];
- B_node<Record, order> *branch[order];///在大多数应用中,这些指针被不同的磁盘中块(block)的地址代替。
- /// constructor:
- B_node();
- };
- template <class Record, int order>
- class B_tree {
- public:
- ////* Add public methods. */
- Error_code search_tree(Record &target);
- Error_code insert(const Record &new_entry);
- Error_code remove(const Record &target);
- protected:
- ////* data members */
- ////* Add protected auxiliary functions here in order to inherit for subclass. */
- ///=============================search=========================================
- Error_code recursive_search_tree(B_node<Record, order> *current, Record &target);
- Error_code search_node(B_node<Record, order> *current, const Record &target, int &position);
- ///=============================insert=========================================
- Error_code push_down(B_node<Record, order> *current,const Record &new_entry,
- Record &median,B_node<Record, order> *&right_branch);
- void push_in(B_node<Record, order> *current, const Record &entry,
- B_node<Record, order> *right_branch, int position);
- void split_node(B_node<Record, order> *current, const Record &extra_entry, B_node<Record, order> *extra_branch,
- int position, B_node<Record, order> *&right_half, Record &median);
- ///==============================remove========================================
- Error_code recursive_remove(B_node<Record, order> *current, const Record &target);
- void remove_data(B_node<Record, order> *current, int position);
- void copy_in_predecessor(B_node<Record, order> *current, int position);
- void restore(B_node<Record, order> *current,int position);
- void move_left(B_node<Record, order> *current, int position);
- void move_right(B_node<Record, order> *current,int position);
- void combine(B_node<Record, order> *current, int position);
- private:
- ////* data members */
- B_node<Record, order> *root;
- ////* Add private auxiliary functions here. */
- };
- #endif //end B_Tree_H_
原文件:(实现B-Tree基本的基本操作)
- /***************************************************************************
- @editor:weedge E-mail:weege@126.com
- @date:2011/08/27
- @comment:
- Data.structures.and.Program.Design.in.Cpp
- Section 11.3:EXTERNALSEARCHING:B-TREES
- 采用泛型编程(模板template),
- 实现对B-TREE结构基本操作的封装。
- 查找:search,插入:insert,删除:remove。
- **********************************************************/
- #include "B_Tree.h"
- template <class Record, int order>
- Error_code B_tree<Record, order>::search_tree(Record &target)
- /*
- Post: If there is an entry in the B-tree whose key matches that in target,
- the parameter target is replaced by the corresponding Record from
- the B-tree and a code of success is returned. Otherwise
- a code of not_present is returned.
- Uses: recursive_search_tree
- */
- {
- return recursive_search_tree(root, target);
- }
- template <class Record, int order>
- Error_code B_tree<Record, order>::recursive_search_tree(
- B_node<Record, order> *current, Record &target)
- /*
- Pre: current is either NULL or points to a subtree of the B_tree.
- Post: If the Key of target is not in the subtree, a code of not_present
- is returned. Otherwise, a code of success is returned and
- target is set to the corresponding Record of the subtree.
- Uses: recursive_search_tree recursively and search_node
- */
- {
- Error_code result = not_present;
- int position;
- if (current != NULL) {
- result = search_node(current, target, position);
- if (result == not_present)
- result = recursive_search_tree(current->branch[position], target);
- else
- target = current->data[position];
- }
- return result;
- }
- template <class Record, int order>
- Error_code B_tree<Record, order>::search_node(
- B_node<Record, order> *current, const Record &target, int &position)
- /*
- Pre: current points to a node of a B_tree.
- Post: If the Key of target is found in *current, then a code of
- success is returned, the parameter position is set to the index
- of target, and the corresponding Record is copied to
- target. Otherwise, a code of not_present is returned, and
- position is set to the branch index on which to continue the search.
- Uses: Methods of class Record.
- */
- {
- position = 0;
- while (position < current->count && target > current->data[position])
- position++; // Perform a sequential search through the keys.
- if (position < current->count && target == current->data[position])
- return success;
- else
- return not_present;
- }
- template <class Record, int order>
- Error_code B_tree<Record, order>::insert(const Record &new_entry)
- /*
- Post: If the Key of new_entry is already in the B_tree,
- a code of duplicate_error is returned.
- Otherwise, a code of success is returned and the Record new_entry
- is inserted into the B-tree in such a way that the properties of a B-tree
- are preserved.
- Uses: Methods of struct B_node and the auxiliary function push_down.
- */
- {
- Record median;
- B_node<Record, order> *right_branch, *new_root;
- Error_code result = push_down(root, new_entry, median, right_branch);
- if (result == overflow) { // The whole tree grows in height.
- // Make a brand new root for the whole B-tree.
- new_root = new B_node<Record, order>;
- new_root->count = 1;
- new_root->data[0] = median;
- new_root->branch[0] = root;
- new_root->branch[1] = right_branch;
- root = new_root;
- result = success;
- }
- return result;
- }
- template <class Record, int order>
- Error_code B_tree<Record, order>::push_down(
- B_node<Record, order> *current,
- const Record &new_entry,
- Record &median,
- B_node<Record, order> *&right_branch)
- /*
- Pre: current is either NULL or points to a node of a B_tree.
- Post: If an entry with a Key matching that of new_entry is in the subtree
- to which current points, a code of duplicate_error is returned.
- Otherwise, new_entry is inserted into the subtree: If this causes the
- height of the subtree to grow, a code of overflow is returned, and the
- Record median is extracted to be reinserted higher in the B-tree,
- together with the subtree right_branch on its right.
- If the height does not grow, a code of success is returned.
- Uses: Functions push_down (called recursively), search_node,
- split_node, and push_in.
- */
- {
- Error_code result;
- int position;
- if (current == NULL) { // Since we cannot insert in an empty tree, the recursion terminates.
- median = new_entry;
- right_branch = NULL;
- result = overflow;
- }
- else { // Search the current node.
- if (search_node(current, new_entry, position) == success)
- result = duplicate_error;
- else {
- Record extra_entry;
- B_node<Record, order> *extra_branch;
- result = push_down(current->branch[position], new_entry,
- extra_entry, extra_branch);
- if (result == overflow) { // Record extra_entry now must be added to current
- if (current->count < order - 1) {
- result = success;
- push_in(current, extra_entry, extra_branch, position);
- }
- else split_node(current, extra_entry, extra_branch, position,
- right_branch, median);
- // Record median and its right_branch will go up to a higher node.
- }
- }
- }
- return result;
- }
- template <class Record, int order>
- void B_tree<Record, order>::push_in(B_node<Record, order> *current,
- const Record &entry, B_node<Record, order> *right_branch, int position)
- /*
- Pre: current points to a node of a B_tree. The node *current is not full
- and entry belongs in *current at index position.
- Post: entry has been inserted along with its right-hand branch
- right_branch into *current at index position.
- */
- {
- for (int i = current->count; i > position; i--) { // Shift all later data to the right.
- current->data[i] = current->data[i - 1];
- current->branch[i + 1] = current->branch[i];
- }
- current->data[position] = entry;
- current->branch[position + 1] = right_branch;
- current->count++;
- }
- template <class Record, int order>
- void B_tree<Record, order>::split_node(
- B_node<Record, order> *current, // node to be split
- const Record &extra_entry, // new entry to insert
- B_node<Record, order> *extra_branch,// subtree on right of extra_entry
- int position, // index in node where extra_entry goes
- B_node<Record, order> *&right_half, // new node for right half of entries
- Record &median) // median entry (in neither half)
- /*
- Pre: current points to a node of a B_tree.
- The node *current is full, but if there were room, the record
- extra_entry with its right-hand pointer extra_branch would belong
- in *current at position position, 0 <= position < order.
- Post: The node *current with extra_entry and pointer extra_branch at
- position position are divided into nodes *current and *right_half
- separated by a Record median.
- Uses: Methods of struct B_node, function push_in.
- */
- {
- right_half = new B_node<Record, order>;
- int mid = order/2; // The entries from mid on will go to right_half.
- if (position <= mid) { // First case: extra_entry belongs in left half.
- for (int i = mid; i < order - 1; i++) { // Move entries to right_half.
- right_half->data[i - mid] = current->data[i];
- right_half->branch[i + 1 - mid] = current->branch[i + 1];
- }
- current->count = mid;
- right_half->count = order - 1 - mid;
- push_in(current, extra_entry, extra_branch, position);
- }
- else { // Second case: extra_entry belongs in right half.
- mid++; // Temporarily leave the median in left half.
- for (int i = mid; i < order - 1; i++) { // Move entries to right_half.
- right_half->data[i - mid] = current->data[i];
- right_half->branch[i + 1 - mid] = current->branch[i + 1];
- }
- current->count = mid;
- right_half->count = order - 1 - mid;
- push_in(right_half, extra_entry, extra_branch, position - mid);
- }
- median = current->data[current->count - 1]; // Remove median from left half.
- right_half->branch[0] = current->branch[current->count];
- current->count--;
- }
- template <class Record, int order>
- Error_code B_tree<Record, order>::remove(const Record &target)
- /*
- Post: If a Record with Key matching that of target belongs to the
- B_tree, a code of success is returned and the corresponding node
- is removed from the B-tree. Otherwise, a code of not_present
- is returned.
- Uses: Function recursive_remove
- */
- {
- Error_code result;
- result = recursive_remove(root, target);
- if (root != NULL && root->count == 0) { // root is now empty.
- B_node<Record, order> *old_root = root;
- root = root->branch[0];
- delete old_root;
- }
- return result;
- }
- template <class Record, int order>
- Error_code B_tree<Record, order>::recursive_remove(
- B_node<Record, order> *current, const Record &target)
- /*
- Pre: current is either NULL or
- points to the root node of a subtree of a B_tree.
- Post: If a Record with Key matching that of target belongs to the subtree,
- a code of success is returned and the corresponding node is removed
- from the subtree so that the properties of a B-tree are maintained.
- Otherwise, a code of not_present is returned.
- Uses: Functions search_node, copy_in_predecessor,
- recursive_remove (recursively), remove_data, and restore.
- */
- {
- Error_code result;
- int position;
- if (current == NULL) result = not_present;
- else {
- if (search_node(current, target, position) == success) { // The target is in the current node.
- result = success;
- if (current->branch[position] != NULL) { // not at a leaf node
- copy_in_predecessor(current, position);
- recursive_remove(current->branch[position],
- current->data[position]);
- }
- else remove_data(current, position); // Remove from a leaf node.
- }
- else result = recursive_remove(current->branch[position], target);
- if (current->branch[position] != NULL)
- if (current->branch[position]->count < (order - 1) / 2)
- restore(current, position);
- }
- return result;
- }
- template <class Record, int order>
- void B_tree<Record, order>::remove_data(B_node<Record, order> *current,
- int position)
- /*
- Pre: current points to a leaf node in a B-tree with an entry at position.
- Post: This entry is removed from *current.
- */
- {
- for (int i = position; i < current->count - 1; i++)
- current->data[i] = current->data[i + 1];
- current->count--;
- }
- template <class Record, int order>
- void B_tree<Record, order>::copy_in_predecessor(
- B_node<Record, order> *current, int position)
- /*
- Pre: current points to a non-leaf node in a B-tree with an entry at position.
- Post: This entry is replaced by its immediate predecessor under order of keys.
- */
- {
- B_node<Record, order> *leaf = current->branch[position]; // First go left from the current entry.
- while (leaf->branch[leaf->count] != NULL)
- leaf = leaf->branch[leaf->count]; // Move as far rightward as possible.
- current->data[position] = leaf->data[leaf->count - 1];
- }
- template <class Record, int order>
- void B_tree<Record, order>::restore(B_node<Record, order> *current,
- int position)
- /*
- Pre: current points to a non-leaf node in a B-tree; the node to which
- current->branch[position] points has one too few entries.
- Post: An entry is taken from elsewhere to restore the minimum number of
- entries in the node to which current->branch[position] points.
- Uses: move_left, move_right, combine.
- */
- {
- if (position == current->count) // case: rightmost branch
- if (current->branch[position - 1]->count > (order - 1) / 2)
- move_right(current, position - 1);
- else
- combine(current, position);
- else if (position == 0) // case: leftmost branch
- if (current->branch[1]->count > (order - 1) / 2)
- move_left(current, 1);
- else
- combine(current, 1);
- else // remaining cases: intermediate branches
- if (current->branch[position - 1]->count > (order - 1) / 2)
- move_right(current, position - 1);
- else if (current->branch[position + 1]->count > (order - 1) / 2)
- move_left(current, position + 1);
- else
- combine(current, position);
- }
- template <class Record, int order>
- void B_tree<Record, order>::move_left(B_node<Record, order> *current,
- int position)
- /*
- Pre: current points to a node in a B-tree with more than the minimum
- number of entries in branch position and one too few entries in branch
- position - 1.
- Post: The leftmost entry from branch position has moved into
- current, which has sent an entry into the branch position - 1.
- */
- {
- B_node<Record, order> *left_branch = current->branch[position - 1],
- *right_branch = current->branch[position];
- left_branch->data[left_branch->count] = current->data[position - 1]; // Take entry from the parent.
- left_branch->branch[++left_branch->count] = right_branch->branch[0];
- current->data[position - 1] = right_branch->data[0]; // Add the right-hand entry to the parent.
- right_branch->count--;
- for (int i = 0; i < right_branch->count; i++) { // Move right-hand entries to fill the hole.
- right_branch->data[i] = right_branch->data[i + 1];
- right_branch->branch[i] = right_branch->branch[i + 1];
- }
- right_branch->branch[right_branch->count] =
- right_branch->branch[right_branch->count + 1];
- }
- template <class Record, int order>
- void B_tree<Record, order>::move_right(B_node<Record, order> *current,
- int position)
- /*
- Pre: current points to a node in a B-tree with more than the minimum
- number of entries in branch position and one too few entries
- in branch position + 1.
- Post: The rightmost entry from branch position has moved into
- current, which has sent an entry into the branch position + 1.
- */
- {
- B_node<Record, order> *right_branch = current->branch[position + 1],
- *left_branch = current->branch[position];
- right_branch->branch[right_branch->count + 1] =
- right_branch->branch[right_branch->count];
- for (int i = right_branch->count ; i > 0; i--) { // Make room for new entry.
- right_branch->data[i] = right_branch->data[i - 1];
- right_branch->branch[i] = right_branch->branch[i - 1];
- }
- right_branch->count++;
- right_branch->data[0] = current->data[position]; // Take entry from parent.
- right_branch->branch[0] = left_branch->branch[left_branch->count--];
- current->data[position] = left_branch->data[left_branch->count];
- }
- template <class Record, int order>
- void B_tree<Record, order>::combine(B_node<Record, order> *current,
- int position)
- /*
- Pre: current points to a node in a B-tree with entries in the branches
- position and position - 1, with too few to move entries.
- Post: The nodes at branches position - 1 and position have been combined
- into one node, which also includes the entry formerly in current at
- index position - 1.
- */
- {
- int i;
- B_node<Record, order> *left_branch = current->branch[position - 1],
- *right_branch = current->branch[position];
- left_branch->data[left_branch->count] = current->data[position - 1];
- left_branch->branch[++left_branch->count] = right_branch->branch[0];
- for (i = 0; i < right_branch->count; i++) {
- left_branch->data[left_branch->count] = right_branch->data[i];
- left_branch->branch[++left_branch->count] =
- right_branch->branch[i + 1];
- }
- current->count--;
- for (i = position - 1; i < current->count; i++) {
- current->data[i] = current->data[i + 1];
- current->branch[i + 1] = current->branch[i + 2];
- }
- delete right_branch;
- }
测试文件:(待写)
//原文地址