反转链表

 

/**
 * 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* reverseBetween(ListNode* head, int left, int right) {
        ListNode* dummyNode = new ListNode(-1);//虚拟结点作为返回使用结点
        dummyNode->next = head;
        ListNode* pre = dummyNode;
         
        for (int i = 0;i < left - 1;i++) {
            pre = pre->next;
        }
        ListNode* next;
        ListNode* cur = pre->next;

        for (int i = 0;i < right - left;i++) {
            next = cur->next;
            cur->next = next->next;
            next->next = pre->next;
            pre->next = next;
        }
        return dummyNode->next;

    }
};