36. 翻转链表 II

翻转链表中第m个节点到第n个节点的部分

样例

给出链表1->2->3->4->5->null， m = 2 和n = 4，返回1->4->3->2->5->null

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param head: ListNode head is the head of the linked list 
     * @param m: An integer
     * @param n: An integer
     * @return: The head of the reversed ListNode
     */
    public ListNode reverseBetween(ListNode head, int m, int n) {
        // write your code here
        ListNode newHead = head;
		ListNode start = head;
		for (int i = 1; i < m; i++) {
			start = head;
			head = head.next;
		}
		ListNode dummy = head;
		for (int i = m; i < n; i++) {
			dummy = dummy.next;
		}
		ListNode end = dummy;
		dummy = dummy.next;
		end.next = null;

		while (head != null) {
			ListNode temp = head.next;
			head.next = dummy;
			dummy = head;
			head = temp;
		}
		if(m == 1) {
		    return dummy;
		}
		start.next = dummy;
		return newHead;
    }
}