leetcode-92-reverse-linked-list-ii

Description

Reverse a linked list from position m to n. Do it in one-pass.

Note: 1 ≤ m ≤ n ≤ length of list.

Example:

1 2	Input: 1->2->3->4->5->NULL, m = 2, n = 4 Output: 1->4->3->2->5->NULL

####

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
     if (m == n) return head;

        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode pNode = dummy;
        ListNode start = head;
        for (int i = 1; i < m; i ++ ) {
            pNode = start;
            start = start.next;
        }for (int i = 0; i < n - m; i ++ ) {

            ListNode temp = start.next;
            start.next = temp.next;
            temp.next = pNode.next;
            pNode.next = temp;
        }
        return dummy.next;
    }
}