https://www.acwing.com/problem/content/1100/

思路：是bfs没错，但是向四周扩展非常玄妙——通过二进制位来确定哪个方向没有墙_(:з」∠)_
注意：dx和dy千万不要写反，而且一定要和方向对上（我因为这个调试半天= =）

#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;

const int maxn = 55;

typedef struct
{
    int x, y;
}P;

int n, m, ans, res;
int a[maxn][maxn];
bool st[maxn][maxn];
int dy[4] = {-1, 0, 1, 0}, dx[4] = {0, -1, 0, 1};

int bfs(int x, int y)
{
    queue<P> q;
    q.push({x, y});
    st[x][y] = true;
    
    int cnt = 0;
    while(q.size())
    {
        P t = q.front();
        q.pop();
        cnt++;
        
        for(int i = 0;i < 4; i++)
        {
            if(!((a[t.x][t.y] >> i) & 1))
            {
                int xx = t.x + dx[i];
                int yy = t.y + dy[i];
                if(xx >= 1 && xx <= n && yy >= 1 && yy <= m && !st[xx][yy])
                {
                    q.push({xx, yy});
                    st[xx][yy] = true;
                }
            }
        }
    }
    
    return cnt;
}

int main()
{
    scanf("%d%d", &n, &m);
    for(int i = 1;i <= n; i++)
        for(int j = 1;j <= m; j++)
            scanf("%d", &a[i][j]);
    
    ans = res = 0;
    for(int i = 1;i <= n; i++)
    {
        for(int j = 1;j <= m; j++)
        {
            if(!st[i][j])
            {
                ans++;
                res = max(res, bfs(i, j));
            }
        }
    }

    printf("%d\n%d\n", ans, res);
    return 0;
}