206 - Reverse Linked List

绿水兰田

于 2019-07-16 13:54:50 发布

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分类专栏： leetcode 文章标签： leetcode 算法

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Problem

Reverse a singly linked list.

Example:

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

Follow up:

A linked list can be reversed either iteratively or recursively. Could you implement both?

Code

/**
 * 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 = head;
        ListNode* pre = NULL;
    	while (cur) {
    	    ListNode* tmp = cur->next;
    	    cur->next = pre;
    	    pre = cur;
    	    if (tmp == NULL) {
    	        break;
    	    }
    	    cur = tmp;
    	}
    	return cur;
    }
};