Last K Sized Group

You are given an array/list ‘ARR’ containing permutation from 1 to 'N' and an integer ‘K’. You have a binary string ‘S’ of size ‘N’ initialised to all zeroes. You perform ‘N’ operations on 'S' as follows:

In the ‘i-th’ operation, you set the ‘ARR[i]-th’ bit of ‘S’ to ‘1’. 

After performing each operation, you get a "group". A "group" of '1s', is a substring of all '1s' in 'S' which can not be extended to its left or right by adding '1s'.

You have to find the last operation when there was a group of size exactly 'K'. If the group of size 'K' was never present, then return -1.

Note :

Both 'ARR' and 'S' are 1 indexed. 

Input Format :

The first line contains a single integer ‘T’ representing the number of test cases. 

The first line of each test case will contain two space-separated integers, ‘N’ and 'K', which denotes the length of the permutation 'ARR', and the required size of the group, respectively. 

The second line of each test case will contain 'N' single space-separated integers, representing the permutation 'ARR'.

Output Format :

For each test case, print the last operation when there was a group of size 'K', else print -1. 

Output for every test case will be printed in a separate line.

Note :

You don’t need to print anything; It has already been taken care of.

Constraints :

1 <= T <= 10
1 <= N <= 100000
1<= K <=N
1<= ARR[i] <= N


Where ‘T’ is the number of test cases, 'N' is the size of the permutation, 'K' is the size of the required group, and 'ARR[i]' is an element of the permutation.

Time limit: 1 sec