双向链表专题

1. 双向链表的结构

注意：这⾥的“带头”跟前面我们说的“头节点”是两个概念，实际前面的在单链表阶段称呼不严
谨，但是为了同学们更好的理解就直接称为单链表的头节点。
带头链表面的头节点，实际为“哨兵位”，哨兵位节点不存储任何有效元素，只是站在这里“放哨
的”。
“哨兵位”存在的意义：
遍历循环链表避免死循环。

2. 双向链表的实现

1 typedef int LTDataType;
2 typedef struct ListNode
3 {
4 struct ListNode* next; //指针保存下⼀个节点的地址
5 struct ListNode* prev; //指针保存前⼀个节点的地址
6 LTDataType data;
7 }LTNode;
8 //void LTInit(LTNode** pphead);
9 LTNode* LTInit();
10 void LTDestroy(LTNode* phead);
11 void LTPrint(LTNode* phead);
12 bool LTEmpty(LTNode* phead);
13 void LTPushBack(LTNode* phead, LTDataType x);
14 void LTPopBack(LTNode* phead);
15 void LTPushFront(LTNode* phead, LTDataType x);
16 void LTPopFront(LTNode* phead);
17 //在pos位置之后插⼊数据
18 void LTInsert(LTNode* pos, LTDataType x);
19 void LTErase(LTNode* pos);
20 LTNode *LTFind(LTNode* phead,LTDataType x);

#define _CRT_SECURE_NO_WARNINGS
#include"list.h"
void LTPrint(LTNode* phead)
{LTNode* pcur = phead->next;while (pcur != phead){printf("%d->", pcur->data);pcur = pcur->next;}printf("\n");
}
//申请节点
LTNode* LTBuyNode(LTDataType x)
{LTNode* node = (LTNode*)malloc(sizeof(LTNode));if (node == NULL){perror("malloc fail");exit(1);}node->data = x;node->next = node->prev = node;return node;
}
//初始化
//void LTInit(LTNode** pphead)
//{
//	//给双向链表创建一个哨兵位
//	*pphead = LTBuyNode(-1);
//
//}
LTNode* LTInit()
{LTNode* phead = LTBuyNode(-1);return phead;
}
//尾插
void LTPushBack(LTNode* phead, LTDataType x)
{assert(phead);LTNode* newnode = LTBuyNode(x);//phead phead->prev newnodenewnode->prev = phead->prev;newnode->next = phead;phead->prev->next = newnode;phead->prev = newnode;
}
//头插
void LTPushFront(LTNode* phead, LTDataType x)
{assert(phead);LTNode* newnode = LTBuyNode(x);newnode->prev = phead;newnode->next = phead->next;phead->next->prev = newnode;phead->next = newnode;
}
//尾删
void LTPopBack(LTNode* phead, LTDataType x)
{//链表必须有效且不能为空assert(phead && phead->next != phead);LTNode* del = phead->prev;del->prev->next = phead;phead->prev = del->prev;//删除delfree(del);del = NULL;}
//头删
void LTPopFront(LTNode* phead, LTDataType x)
{assert(phead && phead->next != phead);LTNode* del = phead->next;phead->next = del->next;del->next->prev = phead;//删除delfree(del);del = NULL;
}
LTNode* LTFind(LTNode* phead, LTDataType x)
{LTNode* pcur = phead->next;while (pcur != phead){if (pcur->data == x){return pcur;}pcur = pcur->next;}//没找到return NULL;
}
//在pos位置之后插入数据
void LTInsert(LTNode* pos, LTDataType x)
{assert(pos);LTNode* newnode = LTBuyNode(x);newnode->next = pos->next;newnode->prev = pos;pos->next->prev = newnode;pos->next = newnode;
}
//删除pos节点
void LTErase(LTNode* pos)
{//pos理论上来说不能为phead，但是没有参数phead，无法增加校验assert(pos);pos->next->prev = pos->prev;pos->prev->next = pos->next;free(pos);pos = NULL;
}
//销毁链表
void LTDesTroy(LTNode* phead)
{assert(phead);LTNode* pcur = phead->next;while (pcur != phead){LTNode* next = pcur->next;free(pcur);pcur = next;}//此时pcur指向pheadfree(phead);phead = NULL;
}

3. 顺序表和双向链表的优缺点分析