题解

#include <bits/stdc++.h>
using namespace std;

int n;
int grid[50][50];
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};

void bfs() {
    queue<pair<int, int>> q;
    for (int i = 0; i <= n + 1; i++) {
        for (int j = 0; j <= n + 1; j++) {
            if ((i == 0 || i == n + 1 || j == 0 || j == n + 1) && grid[i][j] == 0) {
                grid[i][j] = -1;
                q.push({i, j});
            }
        }
    }

    while (!q.empty()) {
        auto [x, y] = q.front(); q.pop();
        for (int i = 0; i < 4; i++) {
            int nx = x + dx[i], ny = y + dy[i];
            if (nx >= 0 && nx <= n + 1 && ny >= 0 && ny <= n + 1 && grid[nx][ny] == 0) {
                grid[nx][ny] = -1;
                q.push({nx, ny});
            }
        }
    }
}

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

    bfs();

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (grid[i][j] == -1) cout << 0 << " ";
            else if (grid[i][j] == 0) cout << 2 << " ";
            else cout << 1 << " ";
        }
        cout << endl;
    }

    return 0;
}