题解 | #腐烂的苹果#

class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param grid int整型vector<vector<>>
     * @return int整型
     */
    int n, m;
    int dx[4] = {1, -1, 0, 0};
    int dy[4] = {0, 0, 1, -1};
    bool vis[1010][1010] = {false};
    int rotApple(vector<vector<int> >& grid) {
        n = grid.size();
        m = grid[0].size();
        queue<pair<int, int>> q;
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++)
                if (grid[i][j] == 2) q.push({i, j});
        int ret = 0;
        while (q.size()) {
            ret++;
            int k = q.size();
            while (k--) {
                auto [x, y] = q.front();
                q.pop();
                for (int i = 0; i < 4; i++) {
                    int a = x + dx[i];
                    int b = y + dy[i];
            if (a < n && a >= 0 && b < m && b >= 0 && !vis[a][b] && grid[a][b] == 1) {
                        vis[a][b] = true;
                        q.push({a, b});
                    }
                }
            }
        }
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++)
                if (grid[i][j] == 1 && !vis[i][j]) return -1;

    return ret-1;

    }

};