Lowest common ancestor BST

Given a binary search tree as a level-order array (None marks a missing child) and two values p and q that are both present, return the value of their lowest common ancestor. Exploit the BST ordering instead of a general-tree LCA: starting at the root, go left when both p and q are smaller than the current node, go right when both are larger, and otherwise the current node is the split point and therefore the LCA. Return the LCA value.