206. Reverse Linked List

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  • Difficulty: Easy
  • Contributors: Admin

Reverse a singly linked list.

Hint:

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

分析

递归版本：
reverseList返回反续后的新头节点
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class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(head == NULL || head->next == NULL) return head;
         
        ListNode* nhead = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return nhead;
    }
};

非递归版本
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class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* dummy = NULL;
        ListNode* pre = dummy;
        ListNode* cur = head;
        ListNode* next;
        while(cur != NULL){
            next = cur->next;
            cur->next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }
};




posted @ 2017-02-15 17:21  copperface  阅读(115)  评论(0)  编辑  收藏  举报