isBST? V3

/* Hidden stub code will pass a root argument to the function below. Complete the function to solve the challenge. Hint: you may want to write one or more helper functions.

The Node struct is defined as follows:
    struct Node {
        int data;
        Node* left;
        Node* right;
    }
*/

#include <limits.h>

void find_max(Node* root, int &res){
    // Base Case
    if (!root)  return;

    // Change result
    res = max(res, root->data);

    // Iterate over all nodes
    find_max(root->right, res);
    find_max(root->left, res);
}

void find_min(Node* root, int &res){
    // Base Case
    if (!root)  return;

    // Change result
    res = min(res, root->data);

    // Iterate over all nodes
    find_min(root->right, res);
    find_min(root->left, res);
}

bool checkBST(Node* root) {
    // Base Case
    if (!root) return true;

    // Find minimum value in tree
    int res_max = INT_MIN;
    find_max(root->left, res_max);

    // Find maximum value in tree
    int res_min = INT_MAX;
    find_min(root->right, res_min);

    // Check if satisfies BST properties
    if(root->left  && res_max >= root->data)    return false;
    if(root->right && res_min <= root->data)    return false;

    // Check if both left and right subtrees are BSTs
    return checkBST(root->right) && checkBST(root->left);
}