백준 14502번 연구소 C++

출처 : https://www.acmicpc.net/problem/14502

 

백트래킹을 이용하여 벽을 3개를 세운 모든 경우를 구하고 각 경우마다 bfs를 통해 바이러스가 퍼지는 것을 시뮬레이션 한 뒤, 그 중 안전지대가 가장 많이 나온 경우를 출력하였다.

 

#include <iostream>
#include <string>
#include <vector>
#include <math.h>
#include <algorithm>
#include <utility>
#include <stack>
#include <queue>
#include <math.h>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>

using namespace std;
typedef long long ll;

int n, m;
vector<vector<int>> v(8, vector<int>(8, 0));
vector<vector<bool>> visited(8, vector<bool>(8, false));
int ans = -1;
int wall = 3;

int posR[4] = { -1,0,1,0 };
int posC[4] = { 0,1,0,-1 };

void BT(int index, int cnt);
int bfs();

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			cin >> v[i][j];
			if (v[i][j] == 1) wall++;
		}
	}
	BT(0, 0);
	cout << ans;
};

void BT(int index, int cnt) {
	if (index >= n * m) return;
	if (cnt == 3) {
		ans = max(ans, bfs());
		return;
	}
	for (int i = index; i < n * m; i++) {
		int row = i / m;
		int col = i % m;
		if (v[row][col] == 0) {
			v[row][col] = 1;
			BT(index + 1, cnt + 1);
			v[row][col] = 0;
		}
	}
}

int bfs() {
	int tmp[8][8];
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			visited[i][j] = false;
			tmp[i][j] = v[i][j];
		}
	}
	int cnt = n * m - wall;
	queue<pair<int, int>> q;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			if (tmp[i][j] == 2 && !visited[i][j]) {
				cnt--;
				q.push({ i,j });
				visited[i][j] = true;
				while (!q.empty()) {
					auto curr = q.front();
					q.pop();
					for (int k = 0; k < 4; k++) {
						int nextRow = curr.first + posR[k];
						int nextCol = curr.second + posC[k];
						if (nextRow < 0 || nextRow >= n) continue;
						if (nextCol < 0 || nextCol >= m) continue;
						if (tmp[nextRow][nextCol] == 1) continue;
						if (visited[nextRow][nextCol]) continue;
						tmp[nextRow][nextCol] = 2;
						q.push({ nextRow, nextCol });
						visited[nextRow][nextCol] = true;
						cnt--;
					}
				}
			}
		}
	}
	return cnt;
}