leetcode206. 反转链表

分析

头插法：

/**
 * 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||!head->next)return head;
        ListNode* dummy=new ListNode();
        dummy->next=nullptr;
        ListNode* cur=head;
        while(cur){
            ListNode* temp=cur;
            cur=cur->next;
            temp->next=dummy->next;
            dummy->next=temp;
        }
        return dummy->next;
    }
};

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||!head->next)return head;
        ListNode*p=reverseList(head->next);
        head->next->next=head;
        head->next=nullptr;
        return p;
    }
};