(LC) 92. Reverse Linked List II

92. Reverse Linked List II

Give you the head pointer head of the singly linked list and two integers left and right, where left <= right. Please reverse the linked list node from position left to position right, and return to the reversed linked list.

Example 1:

Input: head = [1,2,3,4,5], left = 2, right = 4
Output: [1,4,3,2,5]
Example 2:

Input: head = [5], left = 1, right = 1
Output: [5]

prompt:

The number of nodes in the linked list is n
1 <= n <= 500
-500 <= Node.val <= 500
1 <= left <= right <= n

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    
    
    public ListNode reverseBetween(ListNode head, int left, int right) {
    
    
            // 设置 dummyNode 是这一类问题的一般做法
        ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;
        ListNode pre = dummyNode;
        for (int i = 0; i < left - 1; i++) {
    
    
            pre = pre.next;
        }
        ListNode cur = pre.next;
        ListNode 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;
    

    }
}


```