Binary Tree Diameter

• Time : O(n)
• Space : O(d)

using namespace std;

// This is an input class. Do not edit.
class BinaryTree {
public:
  int value;
  BinaryTree *left;
  BinaryTree *right;

  BinaryTree(int value) {
    this->value = value;
    left = nullptr;
    right = nullptr;
  }
};

int helper(BinaryTree *node, int& res) {
	if(!node) return 0;
	int ldepth = helper(node->left, res);
	int rdepth = helper(node->right, res);
	res = max(res, ldepth + rdepth);
	return max(ldepth, rdepth) + 1;
}

int binaryTreeDiameter(BinaryTree *tree) {
	int res = -1;
	helper(tree, res);
	return res;
}