[Round 1B 2017] Problem B. Stable Neigh-bors : https://code.google.com/codejam/contest/8294486/dashboard#s=p1&a=1

Stable Neigh-bors.cc

//
//  Created by fpdjsns
//  Copyright © 2019 fpdjsns. All rights reserved.
//
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>

using namespace std;

/*
 * 시간복잡도 : O(N)
 */

/*
 R = RED 
 O = ORANGE = RED + YELLOW => BOB
 Y = YELLOW
 G = GREEN = YELLOW + BLUE => RGR
 B = BLUE
 V = VIOLET = RED + BLUE => YVY
 */
string solve(int N, int R, int O, int Y, int G, int B, int V) {

	R -= G; Y -= V; B -= O;
	int cnt = (R + Y + B) / 2;
	if (cnt < R || cnt < Y || cnt < B) return "IMPOSSIBLE";
	if (R < 0|| Y < 0 || B < 0) return "IMPOSSIBLE";
	
	string answer = "";
	cnt = (R + Y + B + 1) / 2;
	vector<pair<int, int>> tmp(3);
	tmp[0] = { R, 'R' }; tmp[1] = { Y, 'Y' }; tmp[2] = { B,'B' };
	sort(tmp.begin(), tmp.end());
	int tmpInd = 0;

	for (int i = 0; i < cnt; i++) {
		while (tmp[tmpInd].first <= 0) tmpInd++;
		answer += tmp[tmpInd].second;
		tmp[tmpInd].first--;
		switch (tmp[tmpInd].second) {
		case 'R': R--;  break;
		case 'Y': Y--;  break;
		case 'B': B--;  break;
		}
	}
	int ind = 1;
	while(0 < R + Y + B) {
		while (tmp[tmpInd].first <= 0) tmpInd++;

		tmp[tmpInd].first--;
		switch (tmp[tmpInd].second) {
		case 'R': answer.insert(ind, "R"); R--;  break;
		case 'Y': answer.insert(ind, "Y"); Y--;  break;
		case 'B': answer.insert(ind, "B"); B--;  break;
		}
		ind += 2;
	}

	// mix
	ind = 0;
	while (0 < G + V + O) {
		if (answer.size() == 0) {
			if (0 < G) { answer += "GR"; G--; }
			else if (0 < V) { answer += "VY"; V--; }
			else { answer += "OB"; O--; }
			ind++;
			continue;
		}
		if (answer.size() <= ind)
			return "IMPOSSIBLE";
		if (answer[ind] == 'R') {
			if (0 < G) {
				answer.insert(ind + 1, "GR");
				G--; ind ++;
			}
		}
		else if (answer[ind] == 'Y') {
			if (0 < V) {
				answer.insert(ind + 1, "VY");
				V--; ind ++;
			}

		}
		else if (answer[ind] == 'B') {
			if (0 < O) {
				answer.insert(ind + 1, "OB");
				O--; ind ++;
			}
		}
		ind++;
	}

	return answer;
}


int main() {
	int T;
	cin >> T;
	for (int c = 1; c <= T; c++) {
		int N, R, O, Y, G, B, V;
		cin >> N >> R >> O >> Y >> G >> B >> V;
		string ans = solve(N, R, O, Y, G, B, V);
		printf("Case #%d: ", c);
		cout << ans << endl;
	}
	return 0;
}