Maximum Depth of Binary Tree

 public int maxDepth(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(root ==null) return 0;
       
        return max(maxDepth(root.left) +1, maxDepth(root.right)+1);
    }
   
    public int max(int val1, int val2){
        return val1>val2? val1:val2;
    }