[Algorithm] 17 week(5.02 ~ 5.08) 2/3

938. Range Sum of BST

var rangeSumBST = function(root, low, high) {
    let sum = 0

    if (root === null) {
        return sum
    }
    
    if (root.val > low) {
        sum += rangeSumBST(root.left, low, high)
    }
    if (root.val >= low && root.val <= high) {
        sum += root.val
    }
    if (root.val < high) {
        sum += rangeSumBST(root.right, low, high)
    }
    
    return sum
};