C实现 LeetCode->Reverse Linked List （双指针大法）(单链表反转)

Reverse a singly linked list.

/**

 *  Reverse a singly linked list

   反转单链表，请牢记 Reverse()函数

 */

//
//  ReverseLinkedList.c
//  Algorithms
//
//  Created by TTc on 15/6/22.
//  Copyright (c) 2015年 TTc. All rights reserved.
//
/**
 *  Reverse a singly linked list.
 
   反转单链表，请牢记 Reverse()函数
 */
#include "ReverseLinkedList.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "List.h"


/********************************************************************/
// LeetCode 答案
/********************************************************************/
struct ListNode {
    int val;
    struct ListNode *next;
};

//双指针大法
/*Since only constant memory is allowed, time cost is O(k) */
static struct ListNode*
Reverse(struct ListNode *begin, struct ListNode *end){
    struct ListNode* prev = begin->next;
    struct ListNode* curr = prev->next;
    
    while(curr != end){
        prev->next = curr->next;
        curr->next = begin->next;
        begin->next = curr;
        curr = prev->next;
    }
    return prev;
}

struct ListNode*
reverseList(struct ListNode* head) {
    if(head == NULL || head->next == NULL) return head;
    
    struct ListNode *dummyHead = (struct ListNode *)malloc(sizeof(*dummyHead));
    dummyHead->next = head;
    
    struct ListNode *iter = head;
    
    int count = 1;
    while(iter->next != NULL){
        iter = iter->next;
        ++count;
    }
    Reverse(dummyHead, iter->next);

    return dummyHead->next;
}

/********************************************************************/
/********************************************************************/





/********************************************************************/
// List.c 是范性类 单链表
/********************************************************************/
//反转单链表中  begin  到 end 节点
static ListElmt*
tt_Reverse(ListElmt *begin, ListElmt *end){

    ListElmt* prev = begin->next;
    ListElmt* curr = prev->next;
    
    while(curr != end){
        prev->next = curr->next;
        curr->next = begin->next;
        begin->next = curr;
        curr = prev->next;
    }
    return prev;
}

static ListElmt*
tt_reverseList(ListElmt* head) {
    if(head == NULL || head->next == NULL) return head;
    
    ListElmt *dummyHead = (ListElmt *)malloc(sizeof(*dummyHead));
    dummyHead->next = head;
    
    ListElmt *iter = head;
    int count = 1;
    while(iter->next != NULL){
        iter = iter->next;
        ++count;
    }
    tt_Reverse(dummyHead, iter->next);
    return dummyHead->next;
}

void
test_tt_reverseList(){
    List l1;
    list_init(&l1, free);
    int *data ;
    int array[15] = {100,200,300,400,500,600,700,800,900,1000};
    for (int i = 0; i< 10; i++) {
        if ((data = (int *)malloc(sizeof(int))) == NULL)
            return ;
        *data = array[i];
        if (list_ins_next(&l1, NULL, data) != 0)  //逐个插入元素
            return;
    }
    print_list(&l1);
    ListElmt *result = tt_reverseList(list_head(&l1));
    printf("result->val===%d\n",*(int *)result->data);
    print_listNode(result);
}