1.引子
假如已經從A走到E了, 現在要求從E走到D,用時最短怎么辦?
傳統的循環鏈表只是從A->E->A->D, 但是現在明明可以只要E回退一步就到了D,何必那么麻煩呢
這就需要用到一個指針 告訴E下一步需要走到D, 這個指針就是前驅指針.
也就引入了今天要介紹的雙向鏈表
雙向鏈表是在單鏈表的每個結點中,再設置一個指向其前驅結點的指針。
雙向鏈表
2.代碼
#include <stdio.h>
#include <stdlib.h>
#define OK 1
#define ERROR 0
#define TRUE 1
#define FALSE 0
typedef int Status;
typedef int ElementType;
typedef struct node {
ElementType data;
struct node *prior,*next;
} Node, *DoubleLinkList;
void InitDLLinkList(DoubleLinkList *list) {
*list = (DoubleLinkList)malloc(sizeof(Node));
(*list)->next = NULL;
(*list)->prior = NULL;
}
void createDLinkList(DoubleLinkList list, int n) {
DoubleLinkList p;
p = list;
for (int i = 1; i <= n; i++) {
DoubleLinkList tempNode = (DoubleLinkList)malloc(sizeof(Node));
tempNode->data = i;
//將新結點的next和pror指針 與先后結點都建立關系
p->next = tempNode;
tempNode->prior = p;
p = tempNode;
}
//將最后一個結點的next指向鏈表的頭部, 并將鏈表的前驅指針指向最后一個指針 形成雙向循環鏈表
p->next = list;
list->prior = p;
}
//求雙向鏈表的長度 - 最后一個結點不等于頭結點
int DLLinkLength(DoubleLinkList list) {
int allCount = 0;
DoubleLinkList moveNode = list->next;
while (moveNode != list) {
moveNode = moveNode->next;
allCount++;
}
return allCount;
}
//遍歷 - 正序
void IteratorDLLinkList(DoubleLinkList list) {
DoubleLinkList moveNode = list->next;
int k = 0;
while (moveNode != list) {
printf("current is %d\n",moveNode->data);
moveNode = moveNode->next;
k++;
}
}
//遍歷 - 倒序
void reverse_itemratorList(DoubleLinkList list) {
DoubleLinkList move = list->prior;
int k = 0;
while (move != list) {
printf("current is %d\n",move->data);
move = move->prior;
k++;
}
}
/** 插入情況是考慮已經初始化和創建過鏈表了*/
Status insert_Node_DLList(DoubleLinkList list, int i, ElementType e) {
int length = DLLinkLength(list);
DoubleLinkList insertNode = malloc(sizeof(Node));
insertNode->data = e;
if (i < 0 || i > length+1) {
return ERROR;
}
if (i == 0) {
//1.將新結點的next指向 頭結點的next(即第一個存放數據的結點,此處可能為null)
insertNode->next = list->next;
//2.將頭結點下一個結點的前驅指針 指向當前的插入結點
list->next->prior = insertNode;
//3.將頭結點的next指針指向新結點
list->next = insertNode;
//4.將新節點的前驅指針指向頭結點
insertNode->prior = list;
} else if (i == length+1) {
//0.通過鏈表的前驅結點找到最后一個結點
DoubleLinkList currentLast = list->prior;
//1.將最后一個結點的next指針指向新節點
currentLast->next = insertNode;
//2.將新結點的前驅指針 指向當前最后一個結點
insertNode->prior = currentLast;
//3.因為當前新節點成為了最后一個結點了, 所以新結點的next指針指向頭結點
insertNode->next = list;
//4.將頭結點的前驅指針 指向新結點
list->prior = insertNode;
} else {
int currentIndex;
DoubleLinkList currentNode = list;
//0. 找到第i-1個位置的結點
for (currentIndex = 1; currentIndex < i; currentIndex++) {
currentNode = currentNode->next;
}
//1.將新結點的next指針 指向當前i位置的結點
insertNode->next = currentNode->next;
//2.將當前i位置結點的前驅指針 指向要插入的結點
currentNode->next->prior = insertNode;
//3.將第i-1個位置的next指針 指向新創建的結點
currentNode->next = insertNode;
//4.將新創建結點的前驅指針 指向第i-1個位置的結點
insertNode->prior = currentNode;
}
return OK;
}
/** 刪除(i)結點 相當于直接將 (i-1)結點的指針直接指向第 (i+1)個結點*/
int delete_node(DoubleLinkList list, int k) {
int allCount = DLLinkLength(list);
if (k < 0 || allCount < k) {
return ERROR;
}
DoubleLinkList moveNode = list;
DoubleLinkList deleteNode = list->next;
if (k == 0) {
//頭結點的next指針 直接指向刪除結點的下一個結點
moveNode->next = deleteNode->next;
deleteNode->next->prior = moveNode;
} else if(k == allCount) {
//因為要刪除最后一個結點 所以直接通過頭結點的前驅結點找到要刪除的結點
deleteNode = list->prior;
//根據要刪除的結點的前驅結點 找到第k-1個結點
moveNode = deleteNode->prior;
//剩下兩步是綁定next和前驅指針
moveNode->next = deleteNode->next;
deleteNode->next->prior = moveNode->next;
printf("刪除了");
} else {
//找到第k-1個結點
for (int i = 1; i < k; i++) {
moveNode = moveNode->next;
}
//找到要刪除的第k個結點
deleteNode = moveNode->next;
moveNode->next = deleteNode->next;
deleteNode->next->prior = moveNode;
}
return OK;
}
void print_data(DoubleLinkList list) {
IteratorDLLinkList(list);
printf("length is %d\n",DLLinkLength(list));
printf("\n\n");
}
void print_reverse_data(DoubleLinkList list) {
reverse_itemratorList(list);
printf("length is %d\n",DLLinkLength(list));
printf("\n\n");
}
#pragma mark - 使用
void k_check_DoubleLink(void) {
DoubleLinkList list;
InitDLLinkList(&list);
createDLinkList(list, 9);
insert_Node_DLList(list, 0, 12);
print_data(list);
insert_Node_DLList(list, 5, 22);
print_reverse_data(list);
delete_node(list, 9);
IteratorDLLinkList(list);
}