题解 | #链表内指定区间反转#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @param m int整型 
     * @param n int整型 
     * @return ListNode类
     */
    public ListNode reverseBetween (ListNode head, int m, int n) {
        // write code here
        //哑巴节点减少边际问题
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode pre = dummy;
        //走到节点m-1处
        for(int i = 0;i<m-1;i++){
            pre = pre.next;
        }
        ListNode right = pre;
        //走到节点n处
        for(int j = 0;j<n-m+1;j++){
            right = right.next;
        }
        
        //截取
        ListNode left = pre.next;
        ListNode cur = right.next;
        
        //断开连接
        pre.next = null;
        right.next = null;
        
        //反转
        reverse(left);
        
        //连接
        pre.next = right;
        left.next = cur;
        return dummy.next;
    }
    public ListNode reverse(ListNode head){
        ListNode pre = null;
        ListNode cur = head;
        while(cur != null){
            ListNode flag = cur.next;
            cur.next = pre;
            pre = cur;
            cur = flag;
        }
        return cur;
    }
}