【正经题解】最大黑区域

#include <bits/stdc++.h>
using namespace std;
const int N = 109;
int d[N][N];
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
int n, m;

int dfs(int x, int y) {
    int cnt = 1; // 当前黑区域的像素数
    d[x][y] = 0; // 标记为已访问
    for (int k = 0; k < 4; k++) {
        int nx = x + dx[k], ny = y + dy[k];
        if (nx >= 1 && nx <= n && ny >= 1 && ny <= m && d[nx][ny] == 1) {
            cnt += dfs(nx, ny);
        }
    }
    return cnt;
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            cin >> d[i][j];
        }
    }

    int ans = 0;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (d[i][j] == 1) {
                ans = max(ans, dfs(i, j));
            }
        }
    }

    cout << ans << endl;
    return 0;
}