链表逆序

 (2012-03-08 05:03)

分类：  LinK_List

设链表节点为
typedef struct node {
    int data;
    struct node *next;
}node_t, *pnode_t;

要求将一带链表头List head的单向链表逆序。

分析：

  1). 若链表为空或只有一个元素，则直接返回；

  2). 设置两个前后相邻的指针p,q. 将p所指向的节点作为q指向节点的后继；

  3). 重复2),直到q为空

  4). 调整链表头和链表尾

示例：以逆序A->B->C->D为例，图示如下

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

 #define LEN 10

 typedef struct node {
     int data;
     struct node *pnext;
 } node_t, *pnode_t;

 pnode_t create_link()
 {
     int i;
     pnode_t phead;

     phead = (pnode_t)malloc(sizeof(node_t));
     if (phead == NULL) {
         printf("malloc fail.\n");
         exit(-1);
     }
     memset(phead, 0, sizeof(node_t));

     pnode_t ptail = phead;

     for (i = 0; i < LEN; i++) {
         pnode_t    pnew = (pnode_t)malloc(sizeof(node_t));
         if (pnew == NULL) {
             printf("malloc fail.\n");
             exit(-1);
         }
         memset(pnew, 0, sizeof(node_t));

         pnew->data = i+1;
         pnew->pnext = NULL;
         ptail->pnext = pnew;
         ptail = pnew;
     }

     return phead;
 }

 void print_link(pnode_t phead)
 {
     pnode_t p = phead->pnext;

     while (p != NULL) {
         printf("%d ", p->data);
         p = p->pnext;
     }
     printf("\n");
 }

 void reverse_link(pnode_t phead)
 {
     pnode_t p, q, ptmp;

     p = phead->pnext;
     q = phead->pnext->pnext;
     ptmp = NULL;

     while (q != NULL) {
         ptmp = q->pnext;
         q->pnext = p;
         p = q;
         q = ptmp;
     }

     phead->pnext->pnext = NULL;
     phead->pnext = p;
 }

 int main(int argc, char *argv[])
 {
     pnode_t phead = NULL;

     phead = create_link();

     print_link(phead);

     reverse_link(phead);
     print_link(phead);

     return 0;
 }