双向链表相对于单向链表的优点:
1、单向链表在需要对列表尾部进行操作时,需要通过遍历的方式获取尾部的结点,很浪费时间
2、对于需要频繁使用deleteFromTail()和addToTail()方法的程序,程序效率会非常低
3、双向链表存储了每个结点前面的结点,在对尾部进行操作时,能非常方便的获取尾部的结点信息,方便对尾部进行操作,大大提高了程序效率
4、但是,双向链表比单向链表多存储了一个对象的引用,空间复杂度更高
C++代码:
#include<iostream>
#include<string>
#include<stdio.h>
using namespace std;
//双向链表结点类
class Node{
public:
int value; //结点数据
Node* pre; //前一个结点的指针
Node* next; //后一个结点的指针
//构造函数
Node(int aValue, Node* aPre=0, Node* aNext=0){
value = aValue;
pre = aPre;
next = aNext;
}
};
//双向链表类
class DoublyLinkedList{
public:
Node* head; //链表头
Node* tail; //链表尾
int length; //链表长度
//构造函数
DoublyLinkedList(){
head = tail = 0;
length = 0;
}
//判断链表是否为空
int isEmpty(){
return head == 0;
}
//判断链表是否包含某个值
int contains(int value){
//遍历链表查找值
for (Node* now=head; now!=0; now=now->next)
if (now->value == value)
return true;
return false;
}
//向链表头添加结点
void addToHead(int value){
//如果链表为空,直接添加
if (head == 0)
head = tail = new Node(value, 0, 0);
else
//链表不为空,添加结点,更新head
head = head->pre = new Node(value, 0, head);
length++;
}
//向链表尾添加结点
void addToTail(int value){
//如果链表为空,直接添加
if (head == 0)
head = tail = new Node(value, 0, 0);
//链表不为空,添加结点,更新tail
else
tail = tail->next = new Node(value, tail, 0);
length++;
}
//向指定下标添加结点
void addNode(int value, int index){
//如果指定下标不合法,直接返回
if (index > length+1 || index <= 0) return ;
//如果链表为空,且指定下标不是1,直接返回
if (head==0 && index!=1)
return ;
//如果链表为空,需要新加入结点
if (head==0 && index==1){
head = tail = new Node(value, 0, 0);
//printf("Wrong.....\n");
}
//如果链表不为空,需要在头部加入结点
else if (index==1)
head = head->pre = new Node(value, 0, head);
else {
//链表不为空,在链表中加入结点
int cnt = 0;
Node* aheadOfAdd=head;
//找到要加入结点的前一个结点
for(cnt=1; cnt+1<index; cnt++)
aheadOfAdd = aheadOfAdd->next;
//如果在尾部之后加入结点,更新tail
if (aheadOfAdd == tail)
tail = tail->next = new Node(value, tail, 0);
//否则直接加入
else
aheadOfAdd->next = aheadOfAdd->next->pre = new Node(value, aheadOfAdd, aheadOfAdd->next);
}
length++;
}
//删除链表的第一个结点
int deleteFromHead(){
Node* deletedNode = 0;
int deletedValue = -1;
//如果链表为空,直接返回
if (head == 0)
return -1;
//如果链表只有一个结点,删除这个结点,更新head和tail
if (head == tail)
deletedNode = head;
//正常删除
else{
deletedNode = head;
head = head->next;
head->pre = 0;
}
length--;
deletedValue = deletedNode->value;
delete deletedNode;
return deletedValue;
}
//删除链表的最后一个结点
int deleteFromTail(){
Node* deletedNode = 0;
int deletedValue = -1;
//如果链表为空,直接返回
if (head == 0)
return -1;
//如果链表只有一个结点,删除这个结点,更新head和tail
if (head == tail){
deletedNode = head;
head = tail = 0;
}
//其他情况
else{
deletedNode = tail;
tail = tail->pre;
tail->next = 0;
}
length--;
deletedValue = deletedNode->value;
delete deletedNode;
return deletedValue;
}
//按照给定下标删除结点
int deleteNode(int index){
//如果给定index明显不合法,直接返回
if (index<=0 || index>length)
return -1;
//要删除的结点和被删除的值
Node* deletedNode = head;
int deletedValue = -1;
//如果链表为空,直接返回
if (head == 0) return -1;
//如果链表只有一个元素且要求删除其他的元素,直接返回
if (head == tail && index != 1)
return -1;
//如果链表只有一个元素且要求删除该元素,更新head和tail
if (head == tail && index == 1){
deletedNode = head;
head = tail = 0;
}
//如果需要删除链表头结点
else if(index == 1){
deletedNode = head;
head = head->next;
head->pre = 0;
}
//如果需要删除链表尾结点
else if(index == length){
deletedNode = tail;
tail = tail->pre;
tail->next = 0;
}
//其他情况
else{
int cnt;
for(deletedNode=head,cnt=1; cnt<index; cnt++, deletedNode=deletedNode->next);
deletedNode->pre->next = deletedNode->next;
deletedNode->next->pre = deletedNode->pre;
}
length--;
deletedValue = deletedNode->value;
delete deletedNode;
return deletedValue;
}
//打印链表
//从前向后和从后向前打印,确保前向和后向指针完全正确
void printSelf(){
printf("DoublyLinkedList: [");
for (Node* now=head; now!=0; now=now->next)
printf("%d, ", now->value);
printf("] ");
printf("Backside front: [");
for (Node* now=tail; now!=0; now=now->pre)
printf("%d, ", now->value);
printf("]\n\t\t");
printf("Head: %d\t\ttail: %d\t\tLength: %d\n", head->value, tail->value, length);
}
};
//测试程序
int main(){
DoublyLinkedList* list = new DoublyLinkedList();
list->addToHead(100);list->printSelf();
list->addToHead(200);list->printSelf();
list->addToTail(1);list->printSelf();
list->addToTail(2);list->printSelf();
list->addToTail(3);list->printSelf();
list->deleteFromTail();list->printSelf();
list->deleteFromTail();list->printSelf();
list->addNode(10000, 1);list->printSelf();
printf("\n\n");
list->deleteNode(5);list->printSelf();
printf("%d \n", list->isEmpty());
printf("123456--- %d \n", list->contains(123456));
printf("10000--- %d \n", list->contains(10000));
//list->deleteFromHead();list->printSelf();
//list->deleteFromHead();list->printSelf();
//list->printSelf();
}