147. pair sum in BSt. cpp

#include <bits/stdc++.h> 
/**********************************************************

    Following is the Binary Tree Node structure:

    template <typename T>
    class BinaryTreeNode {
        public: 
        T data;
        BinaryTreeNode<T> *left;
        BinaryTreeNode<T> *right;

        BinaryTreeNode(T data) {
            this->data = data;
            left = NULL;
            right = NULL;
        }

        ~BinaryTreeNode() {
            if (left)
                delete left;
            if (right)
                delete right;
        }
    };
***********************************************************/
void f(BinaryTreeNode<int>* root, vector<int> & inorder){
    if(root==NULL)return;

    f(root->left, inorder);
    inorder.push_back(root->data);
    f(root->right, inorder);
}

bool pairSumBst(BinaryTreeNode<int> *root, int k)
{
    vector<int> inorder;
    f(root, inorder);

    int l = 0, h = inorder.size()-1;
    while(l<h){
        int sum = inorder[l] + inorder[h];
        if(sum==k)return true;
        if(sum<k)l++;
        else h--;
    }
    return false;
}