class Solution {
    int maxi;
    int Depth(TreeNode* root) {
        if (root==nullptr)
            return 0;
        auto dL = Depth(root->left);
        auto dR = Depth(root->right);

        if (maxi < dL+dR+1)
            maxi=dL+dR+1;
        return std::max(dL,dR)+1;
    }
public:
    int diameterOfBinaryTree(TreeNode* root) {
        maxi=0;
        if (root==nullptr)
            return 0;
        return std::max(Depth(root),maxi)-1;
    }
};