Coloring cube

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

#define BR "\n"
#define pb push_back
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<bool> vb;
typedef pair<int, int> ii;

// directions
const int fx[4][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
const int fxx[8][2] = {{0, 1}, {0, -1}, {1, 0},  {-1, 0},
                       {1, 1}, {1, -1}, {-1, 1}, {-1, -1}};

// types
using ll = long long;
using ull = unsigned long long;
using ui = unsigned int;
using us = unsigned short;

const int INF = 1001001001;
const int MAXN = 10000;

int nxt() {
  int x;
  cin >> x;
  return x;
}

int main() {
  // READ("input.txt");

  auto n = nxt();

  string colors = "RGB";
  ll idx = 0;

  if (n % 3 == 0) {
    for (int i = 0; i < n; ++i) {
      for (int j = 0; j < n; ++j) {
        for (int k = 0; k < n; ++k) {
          cout << colors[idx % 3];
          idx++;
        }
        idx--;
        cout << BR;
      }
      idx -= (n - 1);
      cout << BR;
    }
  } else {
    for (int i = 0; i < n; ++i) {
      for (int j = 0; j < n; ++j) {
        for (int k = 0; k < n; ++k) {
          cout << colors[idx % 3];
          idx++;
        }
        cout << BR;
      }
      cout << BR;
    }
  }

  return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED