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Approach: BST walk: go left if both targets are smaller, right if both larger, otherwise current is LCA.

Complexity: O(h) time, O(h) space

js

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {TreeNode}
 */
var lowestCommonAncestor = function(root, p, q) {
    if (!root) {
        return null
    }
    if (root.val > p.val && root.val > q.val) {
        return lowestCommonAncestor(root.left, p, q)
    }
    if (root.val < p.val && root.val < q.val) {
        return lowestCommonAncestor(root.right, p, q)
    }
    return root
};