[백준] 7576번 토마토 C++

https://www.acmicpc.net/problem/7576

#include <iostream>
#include <queue>
using namespace std;

int M, N;

int dy[4] = { 1, 0, -1, 0 };
int dx[4] = { 0, 1, 0, -1 };
int tomato[1001][1001] = { 0, };
queue<pair<int, int>> q;
int next_val = 0;
int bfs_val = 0;
void BFS(int x, int y)
{
	for (int i = 0; i < 4; i++)
	{
		int ny = y + dy[i];
		int nx = x + dx[i];
		if (ny >= 0 && ny < N && nx >= 0 && nx < M && tomato[ny][nx] == 0)
		{
			tomato[ny][nx] = 1;
			next_val++;
			q.push({ nx, ny });
		}
	}
	return;
}

int main(void)
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	
	int tmp;

	cin >> M >> N;
	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < M; j++)
		{
			cin >> tomato[i][j];
			if (tomato[i][j] == 1)
			{
				q.push({ j, i });
			}
		}
	}
	bfs_val = q.size();
	next_val = 0;
	int ret = 0;
	while (!q.empty())
	{
		pair<int, int> start = q.front();
		q.pop();
		BFS(start.first, start.second);
		bfs_val--;
		if (bfs_val == 0)
		{
			bfs_val = next_val;
			next_val = 0;
			ret++;
		}

	}
	ret--;
	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < M; j++)
		{
			if (tomato[i][j] == 0)
				ret = -1;
		}
	}
	cout << ret << "\n";
	return 0;
}