PROG-1166: สวนดอกไม้

#include <bits/stdc++.h>

using namespace std;
using pi = pair <int, int>;
const int N = 30 + 10, M = 30 + 10;
char ar[N][M];
bool vs[N][M];
int di[] = {0, 0, 1, -1};
int dj[] = {1, -1, 0, 0};
int n, m;

bool pst(int i, int j){
    return 1 <= i and i <= n and 1 <= j and j <= m;
}

bool check(int i, int j){
    return ar[i][j] != '#' and
           ar[i][j + 1] != '#' and
           ar[i][j - 1] != '#' and
           ar[i + 1][j] != '#' and
           ar[i - 1][j] != '#';
}

int bfs(int si, int sj, int cnt = 0){
    queue <pi> q;
    q.push({si, sj});
    while(!q.empty()){
        int ui = q.front().first;
        int uj = q.front().second;
        q.pop();
        if(vs[ui][uj]) continue;
        vs[ui][uj] = true;
        cnt ++;
        for(int d=0;d<4;d++){
            int vi = ui + di[d];
            int vj = uj + dj[d];
            if(pst(vi, vj) and !vs[vi][vj] and check(vi, vj))
                q.push({vi, vj});
        }
    }
    return cnt;
}

int main(){

    scanf("%d %d", &n, &m);

    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            scanf(" %c", &ar[i][j]);
        }
    }

    int mx = 0;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(!vs[i][j] and check(i, j))
                mx = max(mx, bfs(i, j));
        }
    }

    printf("%d", mx);

    return 0;
}