树的主要算法有插入，查找，显示，遍历，删除，其中显示和删除略微复杂。
package chap08.tree; import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Stack; class Node { public int iData;
public double dData; public Node leftChild;
public Node rightChild; public void displayNode() {
System.out.print("{" + iData + ", " + dData + "}");
}
} class Tree { // first node of tree
private Node root; public Tree() { root = null;
} /*
* 查找
*/
public Node find(int key) { // (assumes non-empty tree)
Node current = root; // start at root while (current.iData != key) // while no match,
{
if (key < current.iData) {
current = current.leftChild;
}
else {
current = current.rightChild;
}
if (current == null) {
return null;
}
}
return current; // found it
} /*
* 插入
*/
public void insert(int id, double dd) { Node newNode = new Node(); // make new node
newNode.iData = id; // insert data
newNode.dData = dd; if (root == null) { // no node in root
root = newNode;
}
else // root occupied
{
Node current = root; // start at root
Node parent; while (true) // (exits internally)
{
parent = current;
if (id < current.iData) {
current = current.leftChild;
if (current == null) {
// insert on left
parent.leftChild = newNode;
return;
}
}
else {
current = current.rightChild;
if (current == null) {
// insert on right
parent.rightChild = newNode;
return;
}
}
}
}
} /*
* 删除
*/
public boolean delete(int key)
{
// (assumes non-empty list)
Node current = root;
Node parent = root;
boolean isLeftChild = true; // search for node
while (current.iData != key)
{
parent = current;
if (key < current.iData) // go left?
{
isLeftChild = true;
current = current.leftChild;
}
else
{
isLeftChild = false;
current = current.rightChild;
}
if (current == null) // end of the line,
return false; // didn't find it
} // if no children, simply delete it
if (current.leftChild == null && current.rightChild == null) {
if (current == root) {
root = null;
}
else if (isLeftChild) {
parent.leftChild = null; // disconnect
}
else {
// from parent
parent.rightChild = null;
}
} // if no right child, replace with left subtree
else if (current.rightChild == null) {
if (current == root) {
root = current.leftChild;
}
else if (isLeftChild) {
parent.leftChild = current.leftChild;
}
else {
parent.rightChild = current.leftChild;
}
} // if no left child, replace with right subtree
else if (current.leftChild == null)
if (current == root)
root = current.rightChild;
else if (isLeftChild)
parent.leftChild = current.rightChild;
else
parent.rightChild = current.rightChild; // 有两个孩子，则用中序后继替代
else
{
// get successor of node to delete (current)
Node successor = getSuccessor(current); // connect parent of current to successor instead
if (current == root) {
root = successor;
}
else if (isLeftChild) {
parent.leftChild = successor;
}
else {
parent.rightChild = successor;
} // connect successor to current's left child
successor.leftChild = current.leftChild;
} return true;
} /*
* 获取后继
* 返回具有倒数第二高的值的节点
* 找到右孩子，然后右孩子的左子孙
*/
private Node getSuccessor(Node delNode) { Node successorParent = delNode;
Node successor = delNode; // go to right child
Node current = delNode.rightChild; while (current != null) {
successorParent = successor;
successor = current;
// go to left child
current = current.leftChild;
} // if successor not right child
if (successor != delNode.rightChild) { // make connections
successorParent.leftChild = successor.rightChild;
successor.rightChild = delNode.rightChild;
}
return successor;
} public void traverse(int traverseType) {
switch (traverseType) {
case 1:
System.out.print("\nPreorder traversal: ");
preOrder(root);
break;
case 2:
System.out.print("\nInorder traversal: ");
inOrder(root);
break;
case 3:
System.out.print("\nPostorder traversal: ");
postOrder(root);
break;
}
System.out.println();
} /*
* 先序遍历
*/
private void preOrder(Node localRoot) {
if (localRoot != null) {
System.out.print(localRoot.iData + " ");
preOrder(localRoot.leftChild);
preOrder(localRoot.rightChild);
}
} /*
* 中序遍历
*/
private void inOrder(Node localRoot) {
if (localRoot != null) {
inOrder(localRoot.leftChild);
System.out.print(localRoot.iData + " ");
inOrder(localRoot.rightChild);
}
} /*
* 后序遍历
*/
private void postOrder(Node localRoot) {
if (localRoot != null) {
postOrder(localRoot.leftChild);
postOrder(localRoot.rightChild);
System.out.print(localRoot.iData + " ");
}
} /*
* 在控制台打印显示树
*
*/
public void displayTree() { // 全局栈，初始放入树的根节点
Stack globalStack = new Stack();
globalStack.push(root); // 打印空格的数量
int nBlanks = 32; // 是否为空的标识
boolean isRowEmpty = false; while (isRowEmpty == false) { // 本地栈
Stack localStack = new Stack(); // 设置标识为空，后边再根据实际情况判断其是否不为空
isRowEmpty = true; // 打印一定数量的空格，为了将节点 放置在适当的位置以满足视觉效果上树的形状
for (int j = 0; j < nBlanks; j++) {
System.out.print(' ');
} while (globalStack.isEmpty() == false) { // 当标识不为空时，从全局栈弹出栈顶节点
Node temp = (Node) globalStack.pop(); if (temp != null) {
// 如果当前从全局栈弹出的栈顶元素 不为空，则打印当前节点数值，同时将其左右孩子节点放入本地栈
System.out.print(temp.iData);
// 先放左孩子，后方右孩子，后边转移到全局栈后，可以反序，从而保证左孩子在右孩子顶端
localStack.push(temp.leftChild);
localStack.push(temp.rightChild); // 如果当前全局栈弹出的节点有左孩子或右孩子
if (temp.leftChild != null || temp.rightChild != null) {
// 设置标识不为空
isRowEmpty = false;
}
}
else {
// 如果当前从全局栈弹出的栈顶元素 为空，则打印"--"替代节点数值，同时将两个空值放入本地栈
System.out.print("-");
localStack.push(null);
localStack.push(null);
} for (int j = 0; j < nBlanks * 2 - 1; j++) {
System.out.print(' ');
}
} System.out.println();
System.out.println(); nBlanks /= 2; while (localStack.isEmpty() == false) {
// 将本地栈的节点放入全局栈，进行反序，从而保证先处理左孩子
globalStack.push(localStack.pop());
}
}
}
} class TreeApp {
public static void main(String[] args) throws IOException {
int value;
Tree theTree = new Tree(); theTree.insert(50, 1.5);
theTree.insert(25, 1.2);
theTree.insert(75, 1.7);
theTree.insert(12, 1.5);
theTree.insert(37, 1.2);
theTree.insert(43, 1.7);
theTree.insert(30, 1.5);
theTree.insert(33, 1.2);
theTree.insert(87, 1.7);
theTree.insert(93, 1.5); while (true) {
System.out.print("Enter first letter of show, insert, find, delete, or traverse: "); int choice = getChar();
switch (choice) {
case 's':
theTree.displayTree();
break;
case 'i':
System.out.print("Enter value to insert: ");
value = getInt();
theTree.insert(value, value + 0.9);
break;
case 'f':
System.out.print("Enter value to find: ");
value = getInt();
Node found = theTree.find(value);
if (found != null) {
System.out.print("Found: ");
found.displayNode();
System.out.print("\n");
}
else {
System.out.print("Could not find ");
}
System.out.print(value + '\n');
break;
case 'd':
System.out.print("Enter value to delete: ");
value = getInt();
boolean didDelete = theTree.delete(value);
if (didDelete) {
System.out.print("Deleted " + value + '\n');
}
else {
System.out.print("Could not delete ");
}
System.out.print(value + '\n');
break;
case 't':
System.out.print("Enter type 1, 2 or 3: ");
value = getInt();
theTree.traverse(value);
break;
default:
System.out.print("Invalid entry\n");
}
}
} /*
* 获取输入
*/
public static String getString() throws IOException {
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr); String s = br.readLine();
return s;
} public static char getChar() throws IOException {
String s = getString();
return s.charAt(0);
} public static int getInt() throws IOException {
String s = getString();
return Integer.parseInt(s);
}
}