指定区间反转

1.头插法

动画

代码

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @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
        ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;
        ListNode leftPre = dummyNode;//this pointer remains unchanged
        for(int i = 0; i < m-1; i++){
            leftPre = leftPre.next; 
        }
        ListNode curr = leftPre.next;//
        
        for(int i = 1; i <= n-m; i++){
           ListNode next = curr.next;
            curr.next = next.next;
            next.next = leftPre.next;
            leftPre.next = next;
        }
        return dummyNode.next;
    }
}

2.穿针引线法