1254_Number of Closed Islands.cpp

class Solution {
public:
    int closedIsland(vector<vector<int>>& grid) {
        int m = grid.size();
        int n = grid[0].size();
        vector<vector<bool>> visit(m, vector<bool>(n));
        int count = 0;
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(grid[i][j] == 0 && !visit[i][j] && bfs(i, j, m, n, grid, visit)){
                    count++;
                }
            }
        }
        return count;
    }



    bool bfs(int x, int y, int m, int n, vector<vector<int>>& grid, vector<vector<bool>>& visit){
        queue<pair<int,int>> q;
        q.push({x, y});
        visit[x][y] = 2;
        bool isclosed = true;

        vector<int> dirx{0, 1, 0, -1};
        vector<int> diry{-1, 0, 1, 0};

        while(!q.empty()){
            x = q.front().first;
            y = q.front().second;
            q.pop();

            for(int i = 0; i < 4; i++){
                int r = x + dirx[i];
                int c = y + diry[i];
                if(r < 0 || r >= m || c < 0 || c >= n){
                    isclosed = false;
                }
                else if(grid[r][c] == 0 && !visit[r][c]){
                    q.push({r, c});
                    visit[r][c] = true;
                }
            }
        }

        return isclosed;
    }

};