题解

#include<bits/stdc++.h>
using namespace std;
char MAP[1005][1005];
bool vis[1005][1005];
struct node {
    int x, y;
}l, r;
int n, m;
int dir[4][2] = { -1,0,0,1,1,0,0,-1 };
void bfs(int x, int y) {
    queue<node> q;
    q.push({ x,y });
    vis[x][y] = 1;
    while (q.size()) {
        r = q.front();
        q.pop();
        for (int i = 0; i < 4; i++) {
            l.x = r.x + dir[i][0];
            l.y = r.y + dir[i][1];
            if (l.x >= 0 && l.x <= n + 1 && l.y >= 0 && l.y <= m + 1 && !vis[l.x][l.y] && MAP[l.x][l.y] == '0') {
                vis[l.x][l.y] = 1;
                q.push(l);
            }
        }
    }
}
int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        cin >> MAP[i] + 1;
    }
    for (int i = 0; i <= n + 1; i++) {
        for (int j = 0; j <= m + 1; j++) {
            if (i == 0 || j == 0 ||i == n + 1 || j == m + 1) MAP[i][j] = '0';
        }
    }
    bfs(0,0);
    int sum = 0;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (MAP[i][j] == '0' && !vis[i][j]) sum++;
        }
    }
    cout << sum;
    return 0;
}