# Maximum Depth of Binary Tree Problem

## Description

LeetCode Problem 104.

Given the root of a binary tree, return its maximum depth.

A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1:

``````1
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Input: root = [3,9,20,null,null,15,7]
Output: 3
``````

Example 2:

``````1
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Input: root = [1,null,2]
Output: 2
``````

Example 3:

``````1
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Input: root = []
Output: 0
``````

Example 4:

``````1
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Input: root = [0]
Output: 1
``````

Constraints:

• The number of nodes in the tree is in the range [0, 10^4].
• -100 <= Node.val <= 100

## Sample C++ Code

``````1
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class Solution {
public:
int maxDepth(TreeNode* root) {
if (root == NULL)
return 0;
else if ((root->left == NULL) && (root->right == NULL))
return 1;
else if (root->left == NULL)
return maxDepth(root->right) + 1;
else if (root->right == NULL)
return maxDepth(root->left) + 1;
else
return max(maxDepth(root->left), maxDepth(root->right)) + 1;
}
};
``````