26. Reverse linked list II

92. Reverse a linked list II

Give you the head pointer of the single linked list head And two integers left and right , among left <= right . Please reverse from position left To the position right The linked list node of , return Inverted 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]

/** * 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 m, int n) {
    
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode p = dummy;
        ListNode q = dummy;
        for(int i = 0;i < m - 1;i ++) p = p.next;
        for(int i = 0;i < n ;i ++) q = q.next;

        ListNode a = p.next;
        ListNode b = q.next;
        for(ListNode c = p.next,d = c.next;d != b;)
        {
    
            ListNode e = d.next;
            d.next = c;
            c = d;
            d = e;
        }

        a.next = b;
        p.next = q;

        return dummy.next;
    }
}