“秒懂”

#include <bits/stdc++.h>
using namespace std;
const int max_n = 40;
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
int n;
int mp[max_n][max_n];
int vis[max_n][max_n];
struct Node{
    int x, y;
};
void bfs() {
    queue<Node> q;
    for(int i=0;i<n;i++){
        if(mp[0][i]==0){
            q.push({0,i});
            vis[0][i]=1;
        }
        if(mp[n-1][i]==0){
            q.push({n-1,i});
            vis[n-1][i]=1;
        }
        if(mp[i][0]==0){
            q.push({i,0});
            vis[i][0]=1;
        }
        if(mp[i][n-1]==0){
            q.push({i,n-1});
            vis[i][n-1]=1;
        }
    }
    while(!q.empty()){
        Node w=q.front();
        q.pop();
        for(int k=0;k<4;k++){
            int tx=w.x+dx[k];
            int ty=w.y+dy[k];
            if (tx>=0&&tx<n&&ty>=0&&ty<n&&!vis[tx][ty]&&mp[tx][ty]==0){
                vis[tx][ty] = 1;
                q.push({tx, ty});
            }
        }
    }
}
int main(){
    cin >> n;
    for (int i=0;i<n;i++){
        for (int j=0;j<n;j++){
            cin >> mp[i][j];
        }
    }
    bfs();
    for (int i=0;i<n;i++){
        for (int j=0;j<n; j++){
            if (mp[i][j]==0&&!vis[i][j]){
                cout <<2<<" ";
            }else{
                cout <<mp[i][j]<< " ";
            }
        }
        cout << endl;
    }
    return 0;
}