本文双链表介绍部分参考自博文数组、单链表和双链表介绍 以及 双向链表的C/C++/Java实现。
1 双链表介绍
双向链表(双链表)是链表的一种。和单链表一样，双链表也是由节点组成，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。一般我们都构造双向循环链表。
双链表的示意图如下：
表头为空，表头的后继节点为"节点10"(数据为10的节点)；"节点10"的后继节点是"节点20"(数据为10的节点)，"节点20"的前继节点是"节点10"；"节点20"的后继节点是"节点30"，"节点30"的前继节点是"节点20"；...；末尾节点的后继节点是表头。
1.1 双链表添加节点
在"节点10"与"节点20"之间添加"节点15"
添加之前："节点10"的后继节点为"节点20"，"节点20" 的前继节点为"节点10"。
添加之后："节点10"的后继节点为"节点15"，"节点15" 的前继节点为"节点10"。"节点15"的后继节点为"节点20"，"节点20" 的前继节点为"节点15"。
对于“添加节点”功能，在具体实现的时候，我们可以分为三种情况（个人觉得这样逻辑比较清晰，当然有些代码是可以合并的。）：
1）在链表第0位置添加。关键代码如下：
NodePointer ptr = new Node(), prePtr, postPtr;
// assert(ptr != NULL);
ptr->data = val;
if (pos == ) // insert node right behind 'head'
{
postPtr = head->next;
head->next = ptr;
postPtr->pre = ptr; ptr->pre = head;
ptr->next = postPtr;
}
2）在链表最后添加结点（即第len位置，其中len为链表原长度）。关键代码如下：
...
if (pos == ) // insert node right behind 'head'
{
...
}
else if (pos == len) // append node
{
prePtr = head->pre;
head->pre = ptr;
prePtr->next = ptr; ptr->pre = prePtr;
ptr->next = head;
}
3）在链表的中间结点间添加结点。关键代码如下：
...
if (pos == ) // insert node right behind 'head'
{
...
}
else if (pos == len) // append node
{
...
}
else // others
{
prePtr = head->next;
int count = ;
while (prePtr != head && count < pos - )
{
prePtr = prePtr->next;
count++;
}
postPtr = prePtr->next; ptr->next = postPtr;
ptr->pre = prePtr;
prePtr->next = ptr;
postPtr->pre = ptr;
}
1.2 双链表删除节点
删除"节点30"
删除之前："节点20"的后继节点为"节点30"，"节点30" 的前继节点为"节点20"。"节点30"的后继节点为"节点40"，"节点40" 的前继节点为"节点30"。
删除之后："节点20"的后继节点为"节点40"，"节点40" 的前继节点为"节点20"。
对于“添加节点”功能，在具体实现的时候，我们可以分为三种情况：
1）删除链表第1个结点。关键代码如下：
NodePointer ptr, prePtr, postPtr;
if (pos == ) // delete the first node
{
ptr = head->next;
postPtr = ptr->next; head->next = postPtr;
postPtr->pre = head;
delete ptr;
}
2）删除链表最后一个结点。关键代码如下：
...
if (pos == ) // delete the first node
{
...
}
else if (pos == len - ) // delete the last one
{
ptr = head->pre;
prePtr = ptr->pre; prePtr->next = head;
head->pre = prePtr;
delete ptr;
}
3）删除链表的中间结点。关键代码如下：
...
if (pos == ) // delete the first node
{
...
}
else if (pos == len - ) // delete the last one
{
...
}
else // others
{
ptr = head->next;
int count = ;
while (ptr != head && count < pos)
{
ptr = ptr->next;
count++;
}
prePtr = ptr->pre;
postPtr = ptr->next; prePtr->next = postPtr;
postPtr->pre = prePtr;
delete ptr;
}
2. 代码实现
在这里，我设计的类如下：
#ifndef DOUBLELINKEDLIST
#define DOUBLELINKEDLIST #include <iostream>
#include <cassert>
using namespace std; typedef int ElementType;
class Node
{
public:
ElementType data;
Node * pre;
Node * next;
};
typedef Node * NodePointer; class LinkedList
{
public:
LinkedList();
virtual ~LinkedList();
LinkedList(const LinkedList& orig);
LinkedList& operator=(const LinkedList& orig);
bool isEmpty();
bool addNode(const int pos, const ElementType val);
bool deleteNode(const int pos);
void displayNodes();
NodePointer getNode(const int pos);
int getLenOfList(); private:
NodePointer head; }; #endif
相应的实现代码为：
// linkedlist.cpp
#include "linkedlist.h" LinkedList::LinkedList()
{
head = new Node();
//assert(head != NULL);
head->next = head;
head->pre = head;
} LinkedList::~LinkedList()
{
NodePointer ptr = head->next, postPtr;
while (ptr != head)
{
postPtr = ptr;
ptr = ptr->next;
delete postPtr;
}
delete head;
} LinkedList::LinkedList(const LinkedList& orig)
{
// head 初始化这一块不能缺，因为当新声明一个新对象并调用该拷贝构造函数时，
// 新对象的head并不会被初始化，也就没有调用默认构造函数。要不会出错，因为
// 在其他地方有用到了类似ptr = head->next的语句，如在函数getLenOfList（）
// 中，当新对象没有被初始化时，调用该函数就会发生“内存访问错误”。
head = new Node();
//assert(head != NULL);
head->next = head;
head->pre = head; NodePointer ptr = orig.head->next;
int i = ;
while (ptr != orig.head)
{
addNode(i, ptr->data);
ptr = ptr->next;
i++;
} } LinkedList& LinkedList::operator=(const LinkedList& orig)
{
NodePointer ptr = orig.head->next;
int i = ;
while (ptr != orig.head)
{
addNode(i, ptr->data);
ptr = ptr->next;
i++;
} return *this;
} bool LinkedList::isEmpty()
{
return head->next == head && head->pre == head;
} bool LinkedList::addNode(const int pos, const ElementType val)
{
bool isSuccess = true;
int len = getLenOfList();
// assert(0 <= pos <= len);
if (pos < || pos > len)
{
cerr << "The node at position " << pos << " you want to add is less than zero or larger than "
<< "the length of list ." << endl;
isSuccess = false;
throw out_of_range("out_of_range");
}
else
{
NodePointer ptr = new Node(), prePtr, postPtr;
// assert(ptr != NULL);
ptr->data = val;
if (pos == ) // insert node right behind 'head'
{
postPtr = head->next;
head->next = ptr;
postPtr->pre = ptr; ptr->pre = head;
ptr->next = postPtr;
}
else if (pos == len) // append node
{
prePtr = head->pre;
head->pre = ptr;
prePtr->next = ptr; ptr->pre = prePtr;
ptr->next = head;
}
else // others
{
prePtr = head->next;
int count = ;
while (prePtr != head && count < pos - )
{
prePtr = prePtr->next;
count++;
}
postPtr = prePtr->next; ptr->next = postPtr;
ptr->pre = prePtr;
prePtr->next = ptr;
postPtr->pre = ptr;
}
}
return isSuccess;
} bool LinkedList::deleteNode(const int pos)
{
bool isSuccess = true;
int len = getLenOfList();
// assert(0 <= pos <= len);
if (len == )
{
cerr << "There is no elements in the list." << endl;
isSuccess = false;
}
else
{
if (pos < || pos > len - )
{
cerr << "The node at position " << pos << " you want to delete is out of range." << endl;
isSuccess = false;
throw out_of_range("out_of_range");
}
else
{
NodePointer ptr, prePtr, postPtr;
if (pos == ) // delete the first node
{
ptr = head->next;
postPtr = ptr->next; head->next = postPtr;
postPtr->pre = head;
delete ptr;
}
else if (pos == len - ) // delete the last one
{
ptr = head->pre;
prePtr = ptr->pre; prePtr->next = head;
head->pre = prePtr;
delete ptr;
}
else // others
{
ptr = head->next;
int count = ;
while (ptr != head && count < pos)
{
ptr = ptr->next;
count++;
}
prePtr = ptr->pre;
postPtr = ptr->next; prePtr->next = postPtr;
postPtr->pre = prePtr;
delete ptr;
}
}
} return isSuccess;
} void LinkedList::displayNodes()
{
NodePointer ptr = head->next;
while (ptr != head)
{
cout << ptr->data << endl;
ptr = ptr->next;
}
} NodePointer LinkedList::getNode(const int pos)
{
int len = getLenOfList();
if (len == )
{
cerr << "There is no element in the list." << endl;
return NULL;
}
else
{
// assert(0 <= pos <= len);
if (pos < || pos > len - )
{
cerr << "The item at position " << pos << " you want to get is less than zero or "
<< "larger than the length of list." << endl;
throw out_of_range("out_of_range");
// return NULL;
}
else
{
NodePointer ptr = head->next;
int count = ;
while (ptr != head && count < pos)
{
ptr = ptr->next;
count++;
}
return ptr;
}
}
} int LinkedList::getLenOfList()
{
NodePointer ptr = head->next;
int len = ;
while (ptr != head)
{
ptr = ptr->next;
len++;
} return len; }
linkedlist.cpp
Boost单元测试代码为：
#define BOOST_TEST_MODULE LinkedList_Test_Module #include "stdafx.h"
#include "..\DoubleLinkedList\linkedlist.h" struct LinkedList_Fixture
{
public:
LinkedList_Fixture()
{
testLinkedList = new LinkedList();
}
~LinkedList_Fixture()
{
delete testLinkedList;
} LinkedList * testLinkedList;
}; BOOST_FIXTURE_TEST_SUITE(LinkedList_Test_Suite, LinkedList_Fixture) BOOST_AUTO_TEST_CASE(LinkedList_Normal_Test)
{
// isEmpty --------------------------------------------
BOOST_REQUIRE(testLinkedList->isEmpty() == true); // getLenOfList ---------------------------------------
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); // addNode & getNode ---------------------------------
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE((testLinkedList->getNode())->data == );
BOOST_REQUIRE((testLinkedList->getNode())->pre != NULL);
BOOST_REQUIRE((testLinkedList->getNode())->next != NULL);
BOOST_REQUIRE(testLinkedList->isEmpty() == false);
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE((testLinkedList->getNode())->data == );
BOOST_REQUIRE((testLinkedList->getNode())->pre != NULL);
BOOST_REQUIRE((testLinkedList->getNode())->next != NULL);
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE((testLinkedList->getNode())->data == );
BOOST_REQUIRE((testLinkedList->getNode())->pre != NULL);
BOOST_REQUIRE((testLinkedList->getNode())->next != NULL);
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); // deleteNode -----------------------------------------
BOOST_REQUIRE(testLinkedList->deleteNode() == true);
BOOST_REQUIRE((testLinkedList->getNode())->data == );
BOOST_REQUIRE((testLinkedList->getNode())->pre != NULL);
BOOST_REQUIRE((testLinkedList->getNode())->next != NULL);
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); BOOST_REQUIRE(testLinkedList->deleteNode() == true);
BOOST_REQUIRE((testLinkedList->getNode())->data == );
BOOST_REQUIRE((testLinkedList->getNode())->pre != NULL);
BOOST_REQUIRE((testLinkedList->getNode())->next != NULL);
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); BOOST_REQUIRE(testLinkedList->deleteNode() == true);
BOOST_REQUIRE(testLinkedList->getLenOfList() == ); } BOOST_AUTO_TEST_CASE(LinkedList_Abnormal_Test)
{
// initialize ------------------------------------------
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE(testLinkedList->addNode(, ) == true); // addNode -------------------------------------------
BOOST_REQUIRE_THROW(testLinkedList->addNode(-, ), out_of_range);
BOOST_REQUIRE_THROW(testLinkedList->addNode(, ), out_of_range); // deleteNode ----------------------------------------
BOOST_REQUIRE_THROW(testLinkedList->deleteNode(-), out_of_range);
BOOST_REQUIRE_THROW(testLinkedList->deleteNode(), out_of_range); // getNode --------------------------------------------
BOOST_REQUIRE_THROW(testLinkedList->getNode(-), out_of_range);
BOOST_REQUIRE_THROW(testLinkedList->getNode(), out_of_range);
} BOOST_AUTO_TEST_CASE(LinkedList_CopyConstructor_Test)
{
// initialize ------------------------------------------
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE(testLinkedList->addNode(, ) == true); // check copy constructor ------------------------------
LinkedList * testLinkedList2 = new LinkedList(*testLinkedList);
BOOST_REQUIRE(testLinkedList2->isEmpty() == false);
BOOST_REQUIRE(testLinkedList2->getLenOfList() == );
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE((testLinkedList2->getNode())->data == ); BOOST_REQUIRE(testLinkedList2->deleteNode() == true);
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE(testLinkedList2->getLenOfList() == ); BOOST_REQUIRE(testLinkedList2->deleteNode() == true);
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE(testLinkedList2->getLenOfList() == ); BOOST_REQUIRE(testLinkedList2->deleteNode() == true);
BOOST_REQUIRE(testLinkedList2->getLenOfList() == );
} BOOST_AUTO_TEST_CASE(LinkedList_EqualOperator_Test)
{
// initialize ------------------------------------------
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE(testLinkedList->addNode(, ) == true);
BOOST_REQUIRE(testLinkedList->addNode(, ) == true); // check copy constructor ------------------------------
LinkedList * testLinkedList2 = new LinkedList();
*testLinkedList2 = *testLinkedList;
BOOST_REQUIRE(testLinkedList2->isEmpty() == false);
BOOST_REQUIRE(testLinkedList2->getLenOfList() == );
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE((testLinkedList2->getNode())->data == ); BOOST_REQUIRE(testLinkedList2->deleteNode() == true);
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE(testLinkedList2->getLenOfList() == ); BOOST_REQUIRE(testLinkedList2->deleteNode() == true);
BOOST_REQUIRE((testLinkedList2->getNode())->data == );
BOOST_REQUIRE(testLinkedList2->getLenOfList() == ); BOOST_REQUIRE(testLinkedList2->deleteNode() == true);
BOOST_REQUIRE(testLinkedList2->getLenOfList() == );
} BOOST_AUTO_TEST_SUITE_END()
BoostUnitTest.cpp
本篇博文的代码均托管到Taocode : http://code.taobao.org/p/datastructureandalgorithm/src/.