REALLY_COOL_Triangle

#include <iostream>
#include <vector>
#include <cmath>
using namespace std;
int main()
{
    long long int n,i,j,m;
    cin >> n;
    vector < vector<long long int>> a(n, vector<long long int>(n));
    for (i=0;i<n;++i)
        for(j=0;j<n;++j)
            cin >> a[i][j];
    for (i=0;i<n;++i){
        for (j=0;j<n;++j)
        {
            if (i<=n-j-1)
            {
                printf("%2d",a[i][j]);
                cout<<" ";
            }
        }
        cout<<endl;
    }
    return 0;
}