题解 | 剪纸游戏

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <queue>
#include <climits>
using namespace std;

const int dx[4] = { 0, 0, 1, -1 };
const int dy[4] = { 1, -1, 0, 0 };

int n, m;
char arr[1005][1005];
bool visited[1005][1005];

int main() {
    scanf("%d%d", &n, &m);
    getchar(); // 读取换行

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            scanf("%c", &arr[i][j]);
        }
        getchar(); // 读取每行末尾的换行
    }
    int ans = 0;
    // 遍历所有格子
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            // 找到未访问的被剪去的格子，开始BFS
            if (arr[i][j] == '.' && !visited[i][j]) {
                queue<pair<int, int>> q;
                q.push({ i, j });
                visited[i][j] = true;
                int cnt = 1;
                int min_r = i, max_r = i;
                int min_c = j, max_c = j;
                // BFS遍历连通块
                while (!q.empty()) {
                    auto cur = q.front();
                    q.pop();
                    int x = cur.first;
                    int y = cur.second;

                    // 更新连通块的边界
                    if (x < min_r) min_r = x;
                    if (x > max_r) max_r = x;
                    if (y < min_c) min_c = y;
                    if (y > max_c) max_c = y;

                    // 遍历四个方向
                    for (int k = 0; k < 4; k++) {
                        int nx = x + dx[k];
                        int ny = y + dy[k];
                        // 边界检查 + 未访问 + 是被剪去的格子
                        if (nx >= 1 && nx <= n && ny >= 1 && ny <= m
                                && arr[nx][ny] == '.' && !visited[nx][ny]) {
                            visited[nx][ny] = true;
                            q.push({ nx, ny });
                            cnt++;
                        }
                    }
                }
                // 计算包围矩形的面积
                int area = (max_r - min_r + 1) * (max_c - min_c + 1);
                // 若实际格子数等于矩形面积，则为长方形
                if (cnt == area) {
                    ans++;
                }
            }
        }
    }
    printf("%d\n", ans);
    return 0;
}