Reverse Linked List II

Reverse Linked List II

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

For 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.

Java代码：

/** * 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 (head == null || m == n) {        return head;    }    ListNode dummy = new ListNode(0);    dummy.next = head;    head = dummy;    for (int i = 1; i < m; i++) {        head = head.next;    }    ListNode mNode = head.next;    ListNode nNode = mNode, postnNode = mNode.next;    for (int i = m; i < n; i++) {        nNode.next = postnNode.next;        head.next = postnNode;        postnNode.next = mNode;        mNode = head.next;        postnNode = nNode.next;    }    return dummy.next;    }}