Problem Description

Given a sequence of $n$ Christmas lights with specific colors $a_i$ and an integer $k$.

You need to select a continuous segment of these lights such that it can be exactly divided into $k$ subsegments, each with the same color.

If there is a valid selection, output the color of each subsegment; otherwise, output $-1$.

Input Format

The first line contains two positive integers $n$ and $k$.

The second line contains $n$ positive integers $a_i$, representing the colors of the Christmas lights.

Output Format

If there is no valid selection, output $-1$.

Otherwise, output the length of each subsegment in the first line, and the colors of each subsegment in the second line in order. If there are multiple valid selections, output any one of them.

Sample Input and Output

Sample Input #1

8 6
10 1 1 1 1 1 1 5

Sample Output #1

1
1

Sample Input #2

3 2
1 2 1

Sample Output #2

-1

Sample Input #3

10 2
1 5 1 5 2 5 6 2 5 6

Sample Output #3

2
1 5

Notes

Explanation for Sample 3

Select the first four lights $1,5;1,5$ or the last six lights $2,5,6;2,5,6$.

Data Range and Constraints

This problem uses subtask-based testing.

• Subtask 1 (10 pts): Guaranteed to have $k$ consecutive lights of the same color.
• Subtask 2 (15 pts): $k=2$.
• Subtask 3 (25 pts): No special restrictions.

For $100\%$ of the data, $1 \le k \le n \le 50$, $1 \le a_i \le 1000$.

Hints and Notes

To handle multiple solutions, this problem uses a custom Special Judge. Feel free to hack.

This problem is translated from COCI 2021-2022 CONTEST #3 Task 1 Lampice.

The score is set according to the original COCI problem, with a maximum of $50$ points.

见题面 Input 部分

见题面 Output 部分