[蓝桥杯][2018年第九届真题]全球变暖（BFS）

#include<iostream>
#include<queue>
#define MAXN 1001

using namespace std;
int n;
char img[MAXN][MAXN];
bool vis[MAXN][MAXN];
int dx[] = { -1,0,1,0 }, dy[] = { 0, 1, 0, -1 };
/*
7
.......
.##....
.##....
....##.
..####.
...###.
.......
*/

void bfs(int i, int j, int &sum, int &bound) {
    vis[i][j] = true;
    queue<pair<int, int>>q;
    pair<int, int> p(i, j);
    q.push(p);
    while (!q.empty()) {
        auto l = q.front();
        q.pop();
        sum++;
        bool is_bound = false;
        for (int k = 0; k < 4; k++) {
            int x = l.first + dx[k], y = l.second + dy[k];
            if (x > n || y > n || x < 0 || y < 0 || vis[x][y]==true)continue;
            else if (img[x][y] == ‘#‘) {
                vis[x][y] = true;
                p = make_pair(x, y);
                q.push(p);
            }
            else if (img[x][y] == ‘.‘) {
                is_bound = true;
            }
            
        }
        if (is_bound == true)bound++;
    }
}


int main() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> img[i][j];
        }
    }
    int count = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (img[i][j] == ‘#‘ && vis[i][j] == false) {
                int sum = 0, bound = 0;
                bfs(i, j, sum, bound);
                if (sum == bound)count++;
            }
        }
    }
    cout << count;
    return 0;
}