题解 | 链表内指定区间反转

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 dummy = new ListNode(-1);
        ListNode ptrDummy = dummy;
        ListNode ptr = head;
        int i = 1;
        ListNode toInsert;
        while (ptr != null) {
            toInsert = ptr;
            ptr = ptr.next;
            toInsert.next = null;
            if (i < m) {
                ptrDummy.next = toInsert;
                ptrDummy = ptrDummy.next;
            } else if (i <= n) {
                toInsert.next = ptrDummy.next;
                ptrDummy.next = toInsert;
            } else {
                while (ptrDummy.next != null) ptrDummy = ptrDummy.next;
                ptrDummy.next = toInsert;
                ptrDummy = ptrDummy.next;
            }
            i++;
        }
        return dummy.next;
    }
}