In a BST, the LCA is the first node whose value is between p.val and q.val. If both p and q are smaller than the root, the LCA must be in the left subtree. If both are larger, it's in the right subtree.

1. Start at the root.
2. While curr is not None:
   • If p.val and q.val are both smaller than curr.val, move curr = curr.left.
   • Else if p.val and q.val are both larger than curr.val, move curr = curr.right.
   • Otherwise, curr is the LCA. return curr.

• Time Complexity: O(H).
• Space Complexity: O(1).

def lowest_common_ancestor_bst(root, p, q):
    curr = root
    while curr:
        if p.val < curr.val and q.val < curr.val:
            curr = curr.left
        elif p.val > curr.val and q.val > curr.val:
            curr = curr.right
        else:
            return curr