题解 | #链表内指定区间反转# 反转一下

import java.util.*;

public class Solution {
    public ListNode reverseBetween (ListNode head, int m, int n) {
        if(head == null || head.next == null) return head;
        ListNode ret = head;
        ListNode pre = null,next = null;
        for(int i=1; i<m; i++){
            pre = head;
            next = head.next;
            head = head.next;
        }
        
        ListNode tempHead = head, tempPre = pre;
        boolean flag = false;
        for(int j=m-1; j<n; j++) {
            next = head.next;
            head.next = pre;
            pre = head;
            head = next;
            flag = true;
        }
        if(tempPre != null) {
            tempPre.next = pre;
        }
        if(flag) {
            tempHead.next = next;
        }
        if(m > 1) {
            return ret;
        }
        return pre;
    }
}