From https://www.hackerrank.com/contests/projecteuler/challenges/euler004/submissions/code/1302145538

HR_cpp_Euler4.cpp

int main(){
    int t;
    cin >> t;
    vector<long> p;
    for (int a=100001; a < 900010; a+=100001)
        for (int b = 0; b < 90091; b+=10010)
            for (int c = 0; c < 9901; c+=1100)
                    p.push_back(a + b + c);
    sort(p.begin(), p.end());
    p.push_back (0);

    vector<long> xx;
    for(int x = 100; x < 1000; ++x){
        for (int y = 100; y < x; ++y){
            long xy = x * y;
            if (binary_search(p.begin(),p.end(),xy))
                xx.push_back(xy);
        }
    }
    sort(xx.begin(),xx.end());

    for(int a0 = 0; a0 < t; a0++){
        long n;
        cin >> n;
        vector<long>::iterator ans = lower_bound(xx.begin(),xx.end(),n) - 1;
        cout << *ans << endl;
    }
    return 0;
}