题意：
原题链接
代码：
1
、
1、
1、递归
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
if(head == NULL || head->next == NULL) return head;
ListNode *next_tail = head->next;
ListNode *next_head = reverseList(head->next);
next_tail->next = head;
head->next = NULL;
return next_head;
}
};
2
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2、
2、迭代
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
if(head == NULL || head->next == NULL) return head;
ListNode *pre = NULL, *cur = head;
while(cur) {
ListNode* next = cur->next;
cur->next = pre;
pre = cur;
cur = next;
}
return pre;
}
};
