Subtrees Within Range

• Time : O(n)
• Space : O(1)

class BST {
public:
    int value;
    BST *left;
    BST *right;

    BST(int value) {
        this->value = value;
        this->left = nullptr;
        this->right = nullptr;
    }
};
bool helper(BST* t, int l, int r, int s, int e, int& res) {
    if(!t) return true;
    if(l > e or r < s) return false;
    bool sub = s <= t->value and t->value <= e;
	  sub &= helper(t->left, l, t->value, s, e, res);
	  sub &= helper(t->right, t->value, r, s, e, res);
    if(sub) res++;
    return sub;
}
int subtreesWithinRange(BST *tree, vector<int> targetRange) {
    int res = 0;
    helper(tree, INT_MIN, INT_MAX, min(targetRange[0], targetRange[1]), max(targetRange[0], targetRange[1]), res);
    return res;
}