104. Maximum Depth of Binary Tree

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.

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