C语言学习——单链表

今天学习了单链表的增（创建）删改查的操作。

创建链表，共有头插法、尾插法、和有序插入法（中间插入）三种。

1.头插法创建无头链表（头节点中存数据）：无头链表似乎在其他的操作上会比较麻烦，因为要单独处理头节点的数据。

#include <stdio.h>
#include <stdlib.h>

struct node{
int data;
struct node *next;
};

void link_head_insert(struct node** phead,struct node** ptail,int n){
struct node* pnew = (struct node*)malloc(sizeof(struct node));
memset(pnew, 0, sizeof(struct node));
pnew->data = n;
if (*phead == NULL){
*phead = pnew;
*ptail = pnew;
}
else{
pnew->next = *phead;
*phead = pnew;
}
}

void link_print(struct node* phead){
struct node* pcur;
pcur = phead;
while (pcur != NULL){
printf("%3d ", pcur->data);
pcur = pcur->next;
}
printf("\n");
}

int main(){
struct node *phead, *ptail;
int num;
phead = NULL;
ptail = NULL;
while (scanf("%d", &num) != EOF){
link_head_insert(&phead, &ptail, num);
}
link_print(phead);
reverse(phead);
link_print(phead);

system("pause");
return 0;
}

2.尾插法创建有头链表（头节点中不存数据，仅指向下一个节点的指针）

#include <stdio.h>
#include <stdlib.h>

typedef struct node{
int data;
struct node *pNext;
}Node,*pNode;

pNode creatList(pNode pHead){  //尾插法
int i, len, val;  //len是链表节点数，val是节点data值
pHead = (pNode)malloc(sizeof(Node));  //给头节点分配空间
pNode pTail = pHead;  //定义尾节点，初始化在头节点
pTail->pNext = NULL;  //尾节点的指针为空
printf("请输入节点个数：");
scanf("%d", &len);
for (i = 0; i < len; ++i){
printf("第 %d 个节点的数值：", i + 1);
scanf("%d", &val);
pNode pNew = (pNode)malloc(sizeof(Node));  //为各节点分配空间
pNew->data = val;
pTail->pNext = pNew;
pNew->pNext = NULL;
pTail = pNew;
}
return pHead;
}

void printList(pNode pHead){
pNode p = pHead->pNext;
while (NULL != p){
printf("%d ", p->data);
p = p->pNext;
}
printf("\n");
}

void reverse(struct node* head)//单链表的倒置算法
{
struct node  *p, *q;
p = head->pNext;
head->pNext = NULL;
while (p)
{
q = p->pNext;
p->pNext = head->pNext;
head->pNext = p;
p = q;
}
}

void findReverse4(pNode pHead){  //找出链表的倒数第四个节点：先反转，再顺序读第四个节点
reverse(pHead);
pNode p = pHead->pNext;
int cnt=1;
while (NULL != p){
cnt++;
p = p->pNext;
if (cnt < 4)
continue;
else if (cnt == 4)
printf("%d\n", p->data);
}
if (cnt <= 4)
printf("节点数不足4个\n");
}

void findMid(pNode pHead){  //找出链表的中间节点
pNode p = pHead->pNext;
int cnt = 0, mid;
while (NULL != p){
cnt++;
p = p->pNext;
}
mid = cnt/2;

p = pHead->pNext;
cnt = 0;
while (NULL != p){
if (cnt == mid)
printf("%d\n", p->data);
cnt++;
p = p->pNext;
}
}

//using step1 and step2 here 使用p、q两个指针，p每次向前走一步，q每次向前走两步，若在某个时候p == q，则存在环。
//if exists a loop, then the pointer which use step2 will catch up with the pointer which uses step1
void has_loop(pNode head){
pNode p = head;
pNode q = head;
while (p != NULL && q != NULL){
/*
p = p->next;
(q->next != NULL)
q = q->next->next;
if (p == q)
return 1;
*/
//correct it on 17/11/2012
p = p->pNext;
q = q->pNext;
if (q != NULL)
q = q->pNext;
if (p != NULL && p == q)
printf("has loop\n");
}
printf("no loop\n");
}

int main(){
pNode pHead = NULL;
pHead = creatList(pHead);
printList(pHead);
//reverse(pHead);
//printList(pHead);
//findReverse4(pHead);
//findMid(pHead);
has_loop(pHead);

system("pause");
return 0;
}

有头链表与无头链表的区别：
在遍历元素的时候：

有头：

Node *temp;

temp=head->next; //无头：temp=head;

while(temp!=NULL){

......

temp=temp->next;

}