import math
for _ in range(int(input())):
n,k=map(int,input().split())
p=list(map(int,input().split()))
c=0
for i in range(n):
if (p[i]-i-1)%k!=0:
c+=1
c=math.ceil(c/2)
if c==0:
print(0)
elif c==1:
print(1)
else:
print(-1)#include <bits/stdc++.h>
using namespace std;
int main(){
int t;
cin>>t;
while(t--){
int n,k,c=0,x;
cin>>n>>k;
for(int i=1;i<n+1;i++){
cin>>x;
c+=i%k!=x%k;
}
cout<<((c>2)?-1:c/2)<<endl;
}
}1277C - As Simple as One and Two | 1301A - Three Strings |
460A - Vasya and Socks | 1624C - Division by Two and Permutation |
1288A - Deadline | 1617A - Forbidden Subsequence |
914A - Perfect Squares | 873D - Merge Sort |
1251A - Broken Keyboard | 463B - Caisa and Pylons |
584A - Olesya and Rodion | 799A - Carrot Cakes |
1569B - Chess Tournament | 1047B - Cover Points |
1381B - Unmerge | 1256A - Payment Without Change |
908B - New Year and Buggy Bot | 979A - Pizza Pizza Pizza |
731A - Night at the Museum | 742A - Arpa’s hard exam and Mehrdad’s naive cheat |
1492A - Three swimmers | 1360E - Polygon |
1517D - Explorer Space | 1230B - Ania and Minimizing |
1201A - Important Exam | 676A - Nicholas and Permutation |
431A - Black Square | 474B - Worms |
987B - High School Become Human | 1223A - CME |