[Luogu] p2372 yyy2015c01 challenge perimeter (BFS)

Through the tunnel

count (x,y) The perimeter of the connected block where the coordinates are located .
Perimeter ： Judge whether there are four directions X, Is it across the border? , Statistical answer .

#include <bits/stdc++.h>
#define x first
#define y second
using namespace std;
typedef pair<int,int> pii;
const int N = 2e2 + 10;
char g[N][N];
int n,m;
int x,y;
int ans;
pii q[N*N];
bool st[N][N];
bool vis[N][N];
void bfs(int sx, int sy){
    
	int hh = 0, tt = 0;
	q[0] = {
    sx,sy};
	st[sx][sy] = true;
	while(hh <= tt){
    
		pii t = q[hh++];
		for(int i = t.x - 1; i <= t.x + 1; i++){
    
			for(int j = t.y - 1; j <= t.y + 1; j++){
    
				if(i == t.x && j == t.y) continue;
				if((i < 1 || i > n || j < 1 || j > m )){
    
					if(((i== t.x - 1 && j == t.y) || (i== t.x + 1 && j == t.y) || (i== t.x  && j == t.y + 1) || (i== t.x  && j == t.y - 1))){
    
						ans++;
					}
					continue;
				} 
				if(i < 1 || i > n || j < 1 || j > m) continue;
				if(!st[i][j] && g[i][j] == 'X'){
    
					st[i][j] = true;
					q[++tt] ={
    i,j};
					continue;
				}
				if(((i== t.x - 1 && j == t.y) || (i== t.x + 1 && j == t.y) || (i== t.x  && j == t.y + 1) || (i== t.x  && j == t.y - 1))&& g[i][j] == '.' ){
    
					ans++;
				}
			}
		}
	}
}
int main(){
    
	cin >> n >> m >> x >> y;
	for(int i = 1; i <= n; i++){
    
		for(int j = 1; j <= m; j++){
    
			char c;
			cin >> c;
			g[i][j] = c;
		}
	}
	bfs(x,y);
	cout << ans << endl;
	return 0;
}