P1162 填塗顏色

https://www.luogu.com.cn/problem/P1162

qaq搜尋好抽象啊，蒟蒻表示難以理解，搞半天才做出來一道題，很挫敗www

思路

染色法。找牆壁外的連通塊0，染成新顏色。
注意邊界問題：為了照顧到邊緣的連通塊，我們的範圍要設定為0 ~ n + 1

程式碼

#include <iostream>
#include <algorithm>
#include <queue>

using namespace std;
const int N = 35;
int n;
int a[N][N], b[N][N];
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};
bool vis[N][N];

void dfs (int x, int y) {
    
    for (int i = 0; i < 4; i ++) {
        int xx = x + dx[i], yy = y + dy[i];
        if (xx > n + 1 || xx < 0 || yy > n + 1 || yy < 0 || a[xx][yy]) //這個邊界很玄幻啊
            continue;
        a[xx][yy] = 3;
        dfs (xx, yy);
    }

}

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

    dfs (1, 1);
            
    for (int i = 1; i <= n; i ++){
        for (int j = 1; j <= n; j ++) {
            if (a[i][j] == 0)
                cout << 2 << ' ';
            else if (a[i][j] == 3)
                cout << 0 << ' ';
            else
                cout << 1 << ' ';
        }
    cout << endl;
    }    
}
//找牆外聯通塊