Problem

Given: A positive integer $k \le 20$, a positive integer $n \le 10^4$, and $k$ arrays of size $n$ containing integers from $-10^5$ to $10^5$.

Return: For each array $A[1..n]$, output two different indices $1 \le p < q \le n$ such that $A[p] = -A[q]$ if exist, and "-1" otherwise.

Sample Dataset

4 5
2 -3 4 10 5
8 2 4 -2 -8
-5 2 3 2 -4
5 4 -5 6 8

Sample Output

-1
2 4
-1
1 3