Leetcode 206 Reverse Linked List

Reverse a singly linked list.

 

Hint:

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

 

题目大意：反转单链表

提示：

反转一个链表可以用迭代或者递归的方法。你能都实现吗？

 

递归：

/**
 * 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) {
        //最后一个节点会返回，作为头结点
        if(head == NULL || head -> next == NULL)
            return head;
        //head->next 表示剩下的部分
        ListNode* newHead = reverseList(head -> next);
        head -> next -> next = head;
        head -> next = NULL;
        return newHead;
    }
};

迭代：