【leetcode】链表之206(反转链表)

目录

题目详情

题目解法-双指针

C++代码

python代码 

 题目解法-递归

 C++代码

题目详情

题目解法-双指针

C++代码

class Solution {
public:
    ListNode* reverseList(ListNode* head) 
    { 
        //超时用法
        // ListNode dummy ;
        // dummy.next  = head;
        // while (head!= NULL and head->next != NULL)
        // {
        //     dummy.next =head->next;
        //     head->next = head->next->next;
        //     head->next = dummy.next;
        // }
        // return dummy.next;

        //双指针
        ListNode *cur = NULL;
        ListNode *pre = head;
        while( pre != NULL)
        {
            ListNode *t = pre->next;
            pre->next = cur;
            cur = pre;
            pre = t;
        }
        return cur;
        
    }
};

python代码 

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        cur = ListNode()
        cur= None
        pre = head
        while pre != None:
            # t  = ListNode()
            t = pre.next    #记录pre的下一个
            pre.next = cur  #将pre的下个反向指回cur
            cur  = pre   #迭代到下一个cur
            pre = t      #迭代到下个pre
        
        return cur

 题目解法-递归

 C++代码

class Solution {
public:
    ListNode* reverseList(ListNode* head) 
    { 

        //递归
        if(head == NULL || head->next == NULL)
        {
            return head;
        }
        ListNode * ret = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return ret; 
        
    }
};