public class Solution {
    /**
     * @param grid a boolean 2D matrix
     * @return an integer
     */
    class Coordinate {
        int x;
        int y;
        public Coordinate (int x, int y) {
            this.x = x;
            this.y = y;
        } 
        
    }
    public int numIslands(boolean[][] grid) {
        // Write your code here
        if (grid == null || grid.length == 0 || grid[0] == null || grid[0].length == 0) {
            return 0;
        }
        int count = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j]) {
                    markEdge(grid, i, j);
                    count++;
                }
            }
        }
        return count;
    }
    
    private void markEdge(boolean[][] grid, int x, int y) {
        int[] directX = {0, -1, 1, 0};
        int[] directY = {-1, 0, 0, 1};
        int nRow = grid.length;
        int nCol = grid[0].length;
        Coordinate original = new Coordinate(x, y);
        Queue<Coordinate> q = new LinkedList<Coordinate>();
        q.offer(original);
        while (!q.isEmpty()) {
            Coordinate node = q.poll();
            grid[node.x][node.y] = false; // This means this point has been checked. Since they belong to one queue, mark them as false means we don‘t have to make the count++ except the first time (in the main function, if is not satisified)
            for (int i = 0; i < directX.length; i++) {
                Coordinate neighbor = new Coordinate(node.x + directX[i], node.y + directY[i]);
                //System.out.println(neighbor.x + " " + neighbor.y);
                if (isInBound(neighbor, nRow, nCol) && grid[neighbor.x][neighbor.y]) {
                    q.offer(neighbor);    
                }
            }
        }
    }
    
    private boolean isInBound(Coordinate node, int row, int col) {
        int x = node.x;
        int y = node.y;
        return x >= 0 && x < row && y >= 0 && y < col; 
    }
    
    //Slow way which cause the time limitation
    /*private boolean isInBound(boolean[][] grid, Coordinate node) {
        int nRow = grid.length;
        int nCol = grid[0].length;
        if (node.x < 0 || node.x >= nRow || node.y < 0 || node.y >= nCol) {
            return false;
        }
        return true;
    }*/
}