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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        
        if not root:
            return 0;
        elif not root.left:
            return self.maxDepth(root.right) + 1;
        elif not root.right:
            return self.maxDepth(root.left) + 1;
        else:
            return max(self.maxDepth(root.left),self.maxDepth(root.right)) + 1;
          
          
"""
TESTCASES:
Input:
[]
[1]
[1,1]
[1,null,2]
[1,2,3,null,null,1,2,1,null,null,null,1]

Output:
0
1
2
2
5
"""

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