Please may I know where my solution is going wrong

#1

#include
#include<bits/stdc++.h>
#include
#include
using namespace std;
#define ll long long int
int main()
{
ll t;
cin>>t;
while(t–)
{
ll n;
cin>>n;
ll a[n];
for(ll i=0;i<n;i++)
cin>>a[i];
ll s[n];
ll prev=0;
for(ll i=0;i<n;i++)
{
s[i] = prev+a[i];
prev = s[i];
}

    for(ll i=0;i<n;i++)
        s[i] = s[i]%n;
    /*for(ll i=0;i<n;i++)
        cout<<s[i]<< " ";
    cout<<endl;
    */
    map<ll,ll> cnt;
    for(ll i=0;i<n;i++)
        cnt[s[i]]++;
    /*
    for(ll i=0;i<n;i++)
        cout<<cnt[i]<< " ";
    cout<<endl;
    */
    ll ans=0;
    for(ll i=0;i<n;i++)
    {
        ans+=(cnt[i]*(cnt[i]-1)/2);
    }
    ans+=cnt[0];
    cout<<ans<<endl;
}


return 0;

}

#2

@Adarsh-Bhargav-3064379896964870 your logic of storing previous sum is slighlty incorrect . see this code for storing prefix sum
ll sum =0;

       memset(prefixsum ,0 ,sizeof(prefixsum));

          

          prefixsum[0]=1;

       for(int i=0; i<n ;i++){

            cin>>a[i];

            sum+=a[i];

            sum %= n;

            sum = (sum+n)%n;

            prefixsum[sum]++;     

 }
#3

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