leetcode-92：反转链表 II

输入：head = [1,2,3,4,5], left = 2, right = 4
输出：[1,4,3,2,5]

输入：head = [5], left = 1, right = 1
输出：[5]

/**
 * 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) {
        vector<ListNode*> arr;
        ListNode* cur=head;
        while(cur){
            arr.push_back(cur);
            cur=cur->next;
        }
        left--,right--;
        if(left==0){
            head=arr[right];
        }else{
            arr[left-1]->next=arr[right];
        }
        if(right==arr.size()-1){
            arr[left]->next=nullptr;
        }else{
            arr[left]->next=arr[right+1];
        }
        for(int i=right;i>left;i--){
            arr[i]->next=arr[i-1];
        }
        return head;   
    }
};