Dividing into Groups

#include <bits/stdc++.h>

using namespace std;

#define ll     long long
#define _test   int _TEST; cin>>_TEST; while(_TEST--)
#define pb     push_back


int main()
{

    _test
    {
        ll int n, k;
        cin>>n>>k;

        vector<ll int> a(n);
        for(auto &e: a)
            cin>>e;

        sort(a.rbegin(), a.rend());

        ll int low=0, high=1e18;
        ll int ans = 0;

        auto possible = [&](ll int x)
        {
            ll int tot=0, got=0;
            for(int i=0; i<n; i++)
            {
                if(got == 0)
                {
                    if(a[i] >= x)
                    {
                        tot++;
                        continue;
                    }
                    else
                        got += a[i];
                }
                else
                {
                    got += a[i];
                    if(got >= x)
                    {
                        got -= x;
                        tot++;
                    }
                }
            }

            return (tot>=k);
        };

        while(low <= high)
        {
            ll int mid = (low + high)/2;

            if(possible(mid))
                ans=mid, low=mid+1;
            else
                high=mid-1;
        }

        cout<<ans<<"\n";
    }
}