[백준] 7576 - 토마토(설명X)

#include <cstdio>
#include <queue>
using namespace std;
 
int main() {
    int M, N, max = 1, num = 0;
    scanf("%d %d", &M, &N);
    int** field = new int* [N];
    queue<pair<int, int>> bfs;
    for (int i = 0; i < N; i++)
        field[i] = new int[M] {0, };
 
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            scanf("%d", &field[i][j]);
 
            if (field[i][j] == 1) {
                bfs.push(make_pair(i, j));
                num++;
            }
            else if (field[i][j] == -1)
                num++;
        }
    }
    while (!bfs.empty()) {
        pair<int, int> val = bfs.front();
        bfs.pop();
 
        int next = field[val.first][val.second] + 1;
 
        if (val.first - 1 >= 0 && field[val.first - 1][val.second] == 0) {
            field[val.first - 1][val.second] = next;
            bfs.push(make_pair(val.first - 1, val.second));
            num++; max = next;
        }
        if (val.second + 1 < M && field[val.first][val.second + 1] == 0) {
            field[val.first][val.second + 1] = next;
            bfs.push(make_pair(val.first, val.second + 1));
            num++; max = next;
        }
        if (val.first + 1 < N && field[val.first + 1][val.second] == 0) {
            field[val.first + 1][val.second] = next;
            bfs.push(make_pair(val.first + 1, val.second));
            num++; max = next;
        }
        if (val.second - 1 >= 0 && field[val.first][val.second - 1] == 0) {
            field[val.first][val.second - 1] = next;
            bfs.push(make_pair(val.first, val.second - 1));
            num++; max = next;
        }
    }
    printf("%d\n", num == N * M ? max - 1 : -1);
}