题解 | #牛群的重新排列#

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 left int整型
     * @param right int整型
     * @return ListNode类
     */
    public ListNode reverseBetween (ListNode head, int left, int right) {
        if (left == right)return head;
        // write code here
        ListNode pre = null;
        ListNode end = head;
        ListNode cur = head;
        ListNode pointpre = null;
        for (int i = 1; i < left; i++) {
            if(pointpre==null){pointpre=head;continue;}
            pointpre=pointpre.next;
        }
        for (int i = 0; i < right; i++) {
            end = end.next;
        }
        pre = end;
        if(pointpre!=null){
            cur = pointpre.next;
        }
        while (cur != end) {
            ListNode temp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = temp;
        }
        if (pointpre == null) {
            return pre;
        } else {
            pointpre.next = pre;
        }
        head.next=pointpre;

        return head;
    }
}