#include <bits/stdc++.h>   using namespace std;   int main() {     long long int t, n, k;     cin >> t;     while (t--) {       cin >> n >> k;       long long int a[n];       set<long long int> s;       for (long long int i = 0; i < n; i++) {         cin >> a[i];         s.insert(a[i]);       }       sort(a, a + n);       if (k == 1 && s.size() == 1) {         cout <<  1 n ;         continue;       }       if (k == 1 && s.size() != 1) {         cout <<  -1 n ;         continue;       }       long long int c = 0;       for (long long int i = 0; i < n - 1; i++) {         if (a[i + 1] - a[i] != 0) {           c++;         }       }       long long int o = 1;       cout << max(o, ((c + k - 2) / (k - 1))) <<   n ;     }     return 0;   }   