994 . Oranges

class Solution {
 
    public int orangesRotting(int[][] grid) {
        
        
        if(grid == null || grid.length == 0) return -1;
        
        
        
        
        for(int i=0; i<grid.length; i++) {
            for(int j=0; j<grid[0].length; j++) {
                if(grid[i][j] == 2) {
                    dfs(i, j, grid, 2);
                }
            }
        }
        
        int minutes = 2;
        for(int[] row : grid) {
            for(int cell : row) {
                if(cell == 1) return -1;
                minutes = Math.max(minutes, cell);
            }
        }
        
        return minutes - 2;
    }
    
    private void dfs(int i, int j, int[][] grid, int minutes) {
            
            if(i < 0 || i >= grid.length || j < 0 || j >= grid[0].length || grid[i][j] == 0 || (1 < grid[i][j] && grid[i][j] < minutes)
          ) return;
        else {
            grid[i][j] = minutes;
            dfs(i - 1, j, grid, minutes + 1);
            dfs(i + 1, j, grid, minutes + 1);
            dfs(i, j - 1, grid, minutes + 1);
            dfs(i, j + 1, grid, minutes + 1);
        }    
    }
}