Reverse Linked List II

Source

• lintcode: Reverse Linked List II

Reverse a linked list from position m to n.

Example
Given 1->2->3->4->5->NULL, m = 2 and n = 4, return 1->4->3->2->5->NULL.

Note
Given m, n satisfy the following condition: 1 ≤ m ≤ n ≤ length of list.

Challenge
Reverse it in-place and in one-pass

Java

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param ListNode head is the head of the linked list 
     * @oaram m and n
     * @return: The head of the reversed ListNode
     */
    public ListNode reverseBetween(ListNode head, int m , int n) {
        ListNode dummy = new ListNode(0);    
        dummy.next = head;   
        ListNode pre = dummy;
        ListNode cur=head;    
        int pos=1;

        while(pos<m){
            pre=cur;
            cur=cur.next;
            pos++;    
        }

        while(pos<n){
            ListNode tmp = cur.next.next;    
            cur.next.next = pre.next;    
            pre.next = cur.next;    
            cur.next = tmp;    
            pos++;
        }

        return dummy.next;
    }
}