Diameter of binary tree (Un-optimized)

#include <bits/stdc++.h>

using namespace std;

struct TreeNode

{

    int val;

    TreeNode *left;

    TreeNode *right;

    TreeNode() : val(0), left(nullptr), right(nullptr) {}

    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}

    TreeNode(int x, TreeNode *left, TreeNode *right) : 

                      val(x), left(left), right(right) {}

};

// there will be three cases, the diameter may pass through root

//secondly, the diameter would only be in the left part of rootnode

// or the diameter would only be in right part of root node;

// Note that the root node of subtree is also called root node,

// The diameter of all leaf nodes are zeros,

// and height of every node is retuned in ls or rs,

// which are used to find

// height and then diamater.

TreeNode *BuildTree()

{

    int d;

    cin >> d;

    if (d == -1)

        return NULL;

    TreeNode *Node = new TreeNode(d);

    Node->left = BuildTree();

    Node->right = BuildTree();

    return Node;

}

void print(TreeNode *root)

{

    if (root == NULL)

        return;

    cout << root->val;

    print(root->left);

    print(root->right);

}

int height(TreeNode *root)

{

    if (root == NULL)

        return 0;

    int ls = height(root->left);

    int rs = height(root->right);

    return max(ls, rs) + 1;

}

int diameter(TreeNode *root)

{

    if (root == NULL)

        return 0;

    int lh = height(root->left);

    int rh = height(root->right);

    int op1 = lh + rh;

    int op2 = diameter(root->left);

    int op3 = diameter(root->right);

    return max(op1, max(op2, op3));

}

int main()

{

    TreeNode *root = BuildTree();

    cout << "PreOrder of Tree is: ";

    print(root);

    cout << endl;

    cout << "The daimeter of binary tree : " << diameter(root);

}