package LeetCode;

import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class LC_92 {
    public class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

    public ListNode reverseBetween(ListNode head, int left, int right) {
        if (head == null) return head;
        if (head.next == null) return head;
        if (left == right) return head;
        ListNode befLeft = head;
        ListNode aftRight = null;
        int idx = 1;
        while (idx < left - 1) {
            befLeft = befLeft.next;
            idx++;
        }
        aftRight = befLeft;
        while (idx <= right) {
            aftRight = aftRight.next;
            idx++;
        }
        ListNode pre = befLeft;
        ListNode cur = pre.next;
        while (cur != aftRight) {
            ListNode n = cur.next;
            cur.next = pre;
            pre = cur;
            cur = n;
        }
        befLeft.next.next = aftRight;
        befLeft.next = pre;
        return head;

    }

}