【Leetcode206】 Reverse Linked List

题目

分析

代码

/**
* 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 || !head->next) return head;
ListNode *p=head;
ListNode *head_temp=p->next;
while(head_temp){
ListNode *tmp=head_temp->next;
head_temp->next=p;
p=head_temp;
head_temp=tmp;
}
head->next=NULL;
return p;
}
};

/**
* 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 || !head->next)
return head;
ListNode *new_head=reverseList(head->next);
head->next->next=head;   //串联已逆置部分和head
head->next=NULL;
return new_head;      //返回最底层递归得到的head
}
};