LC 206. Reverse Linked List

题目描述

Reverse a singly linked list.

Example:

Input: 1->2->3->4->5->NULL
Output: 5->4->3->2->1->NULL

参考答案

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* cur = NULL;
        while(head){
            ListNode * temp = head->next;
            head -> next = cur;
            cur = head;
            head = temp;
        }
        return cur;
    }
};

补充说明

term 1:

temp = 2 3 4 5 null

head = 1 null = 1 2 3 4 5 null + null 

cur = 1 null 

head = 2 3 4 5 null 

term 2:

temp = 3 4 5 null

head = 2 1 null （ 2 3 4 5 null + 1 null）

cur = 2 1 null

head = 3 4 5 null

term 3:

temp = 4 5 null

head = 3 2 1 null = 3 4 5 null + 2 1 null

cur = 3 2 1 null

head = 4 5 null

......