Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

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Thought:

Nothing special but..

I’m using Java this time..

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int maxDepth(TreeNode root) {
        return maxDepthHelper(root, 0);
    }
     public int maxDepthHelper(TreeNode node, int depth) {
        if(node != null){
            return Math.max(maxDepthHelper(node.left, depth+1)
                       , maxDepthHelper(node.right, depth+1));
        }
         return depth;
    }
}