Longest subarray with sum divisible by K

#include <bits/stdc++.h>
using namespace std;

int main() {
    int i,j,t,n,k,y;
    cin>>t;
    while(t--)
    {
        cin>>n>>k;
        int a[n],s=0;
        for(i=0;i<n;i++)cin>>a[i];
        int mp[k];
        memset(mp,-1,sizeof(mp));
        int ans=0;
        for(i=0;i<n;i++)
        {
            s+=a[i];
            y=(s%k+k)%k;
            if(mp[y]==-1)mp[y]=i;
            if(y==0)ans=i+1;
            else ans=max(ans,i-mp[y]);
        }
        cout<<ans<<endl;
    }
    return 0;
}