Maximum Depth of Binary Tree

 1 public class Solution {
 2     public int maxDepth(TreeNode root) 
 3     {
 4         int depth=0;
 5         depth=depthHelper(root,depth);
 6         return depth;
 7     }
 8     
 9     public int depthHelper(TreeNode root, int depth)
10     {
11         if(root==null)
12         return 0;
13         
14         depth+=1;
15         if(root.left!=null&&root.right!=null) 
16         {
17            return Math.max(depthHelper(root.left,depth),depthHelper(root.right,depth));
18         }
19         else if (root.left==null&&root.right!=null)
20         {
21             return depthHelper(root.right,depth);
22         }
23         else if(root.left!=null&&root.right==null)
24         {
25             return depthHelper(root.left,depth);
26         }
27         else return depth;
28 
29     }
30 }