LeetCode --- 206. Reverse Linked List丨反转链表

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206. Reverse Linked List

Difficulty: Easy

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?

思路

设⽴立三个指针：cur——当前结点；pre——当前结点的前⼀一个结点；temp——临时结点（标记cur的next）。⾸首先保存cur的next到temp，然后将cur的next指向pre，将pre移动到当前cur，然后将cur指向temp，直到cur==NULL，返回pre即反转了了该链表～

Solution

Language: C++

/**
 * 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) {
        if (head == NULL) return head;
        ListNode *cur = head, *pre = NULL, *temp = NULL;
        while (cur != NULL){
            temp = cur->next;
            cur->next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
};

Language: Python

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        cur, prev = head, None
        while cur:
            cur.next, prev, cur = prev, cur, cur.next
        return prev