rotting-oranges.java

class Solution {
    int rottonCount = 0;
    int totalCount = 0;
    int m,n;
    public int orangesRotting(int[][] grid) {
            m = grid.length;
        n = grid[0].length;
        Queue<Point> kyu = new LinkedList<>();
        for(int i=0;i<m;++i){
            for(int j=0;j<n;++j){
                if(grid[i][j] > 0){
                    totalCount++;
                    if(grid[i][j] == 2){
                        rottonCount++;
                        kyu.add(new Point(i, j));
                    }
                }
            }
        }
        int level = 0;
        // null is delimeter
        kyu.add(null);
        int freshCount = totalCount - rottonCount;


        while(!kyu.isEmpty()){
            Point p = kyu.poll();
            if(Objects.isNull(p)){
                level++;
                if(!kyu.isEmpty()){
                    kyu.add(null);
                }
            } else {
                for(Point t  : getNearbyFresh(p, grid)){
                    freshCount--;
                    kyu.add(t);
                }
            }
        }
        if(freshCount == 0)
            return level-1;
        return -1;
    }
    public List<Point> getNearbyFresh(Point p, int[][] grid){
        int[][] steps = new int[][]{{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
        List<Point> list = new LinkedList<>();
        for(int[] step : steps){
            int x = p.x + step[0];
            int y = p.y + step[1];
            if(x >= 0 && x < m && y>=0&&y < n && grid[x][y]==1){
                grid[x][y] = 2;
                list.add(new Point(x, y));
            }
        }
        return list;
    }

    class Point{
        int x,y;
        Point(int x, int y){
            this.x = x;this.y = y;
        }
        public String toString(){
            return (String.format(" [%s,%s]", x, y ));
        }
    }
}