题解 | 牛群的重新排列

1. 请直接参照牛群的重新分组。

import java.util.*;

public class Solution {
    public void reverseList(ListNode head) {
        ListNode pre = null, cur = head;
        while (cur != null) {
            final ListNode nxt = cur.next;
            cur.next = pre;
            pre = cur;
            cur = nxt;
        }
    }            
    
    public ListNode reverseBetween (ListNode head, int left, int right) {
        ListNode guard = new ListNode(0);
        guard.next = head;
        int cnt = 0;
        ListNode preLeft = guard, cur = head;
        while(cur != null) {
            cnt += 1;
            if (cnt < left) {
                preLeft = cur;
                cur = cur.next;
            } else if (cnt < right) {
                cur = cur.next;
            } else {
                final ListNode nxt = cur.next;
                cur.next = null;
                reverseList(preLeft.next);
                final ListNode rangeTail = preLeft.next;
                preLeft.next = cur;
                rangeTail.next = nxt;
                break;
            }
        }
        return guard.next;
    }
}