Sum

input/code.cpp: In function 'bool tinka(int, int, std::__cxx11::string*, int)':
input/code.cpp:17:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (A.size() == n * m && x == 0 && y == 0)
       ~~~~~~~~~^~~~~~~~
input/code.cpp: In function 'int main()':
input/code.cpp:43:10: warning: unused variable 'pradzia' [-Wunused-variable]
  clock_t pradzia = clock();
          ^~~~~~~

/*input
4 4
*/
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
bool tinka(int n, int m, string a[], int maxi = 100)
{
	int x = 0, y = 0;
	int t = 0;
	set<pair<int, int>>A = {{x, y}};
	while (maxi > 0)
	{
		if (A.size() == n * m && x == 0 && y == 0)
			return true;
		if (x + dx[t] < 0 || y + dy[t] < 0 || x + dx[t] >= n || y + dy[t] >= m)
			return false;
		bool same = (a[x][y] == a[x + dx[t]][y + dy[t]]);
		if (a[x][y] == 'R')
		{
			a[x][y] = 'G';
		}
		else if (a[x][y] == 'G')
		{
			a[x][y] = 'B';
		}
		else
			a[x][y] = 'R';
		x += dx[t];
		y += dy[t];
		if (!same)
			t = (t + 1) % 4;
		A.insert({x, y});
		maxi--;
	}
	return false;
}
int main()
{
	clock_t pradzia = clock();
	srand(2019);
	ios_base::sync_with_stdio(false);
	int n, m;
	cin >> n >> m;
	{
		if (n == 2)
		{
			for (int t = 0; t < m; t++)
			{
				if (t < m - 1)
					cout << "R";
				else
					cout << "B\n";
			}
			for (int t = 0; t < m; t++)
			{
				if (t < m - 1)
				{
					if (t == 0)
						cout << "B";
					else
						cout << "G";
				}
				else
					cout << "G\n";
			}
			return 0;
		}
		if (m == 2)
		{
			cout << "RB\n";
			for (int i = 0; i < n - 2; i++)
				cout << "RB\n";
			cout << "RG\n";
			return 0;
		}
	}
	string x[2] = {
		"RRRB",
		"BGGG"
	};
	ll W = 0;
	while (W <= pow(3, (n * m)))
	{
		if (W % 2000 == 0)
		{
			cout << W / pow(3, (n * m)) << endl;
		}
		W++;
		string a[n];
		ll WW = W;
		for (int i = 0; i < n; i++)
		{
			a[i] = string(m, 'R');
			for (int t = 0; t < m; t++)
			{
				if (W % 3 == 0)
				{
					a[i][t] = 'R';
				}
				else if (W % 3 == 1)
				{
					a[i][t] = 'G';
				}
				else
					a[i][t] = 'B';
				W /= 3;
			}
		}
		W = WW;
		string b[n];
		for (int i = 0; i < n; i++)
		{
			b[i] = a[i];
		}
		if (tinka(n, m, a))
		{
			for (int i = 0; i < n; i++)
				cout << b[i] << "\n";
			return 0;
		}
	}
	cout << "IMPOSSIBLE\n";
}

Test 1

Verdict: TIME LIMIT EXCEEDED

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: TIME LIMIT EXCEEDED

Test 4

Verdict: TIME LIMIT EXCEEDED

Test 5

Verdict: TIME LIMIT EXCEEDED

Test 6

Verdict: TIME LIMIT EXCEEDED

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: TIME LIMIT EXCEEDED

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: TIME LIMIT EXCEEDED

Test 12

Verdict: TIME LIMIT EXCEEDED

Test 13

Verdict: TIME LIMIT EXCEEDED

Test 14

Verdict: TIME LIMIT EXCEEDED

Test 15

Verdict: TIME LIMIT EXCEEDED

Test 16

Verdict: TIME LIMIT EXCEEDED

Test 17

Verdict: TIME LIMIT EXCEEDED

Test 18

Verdict: TIME LIMIT EXCEEDED

Test 19

Verdict: TIME LIMIT EXCEEDED

Test 20

Verdict: TIME LIMIT EXCEEDED

Test 21

Verdict: TIME LIMIT EXCEEDED

Test 22

Verdict: TIME LIMIT EXCEEDED

Test 23

Verdict: TIME LIMIT EXCEEDED

Test 24

Verdict: TIME LIMIT EXCEEDED

Test 25

Verdict: TIME LIMIT EXCEEDED

Test 26

Verdict: TIME LIMIT EXCEEDED

Test 27

Verdict: TIME LIMIT EXCEEDED

Test 28

Verdict: TIME LIMIT EXCEEDED