Maximum Depth of Binary Tree LeetCode solution in C++

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