Diameter of Binary Tree LeetCode solution in C++

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class Solution {
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 public:
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  int diameterOfBinaryTree(TreeNode *root) {
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    int diameter = 0;
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    height(root, diameter);
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    return diameter;
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  }
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 private:
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  int height(TreeNode *node, int &diameter) {
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    if (!node) {
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      return 0;
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    }
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    int lh = height(node->left, diameter);
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    int rh = height(node->right, diameter);
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    diameter = max(diameter, lh + rh);
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    return 1 + max(lh, rh);
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  }
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};