235-lcaBST.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.val > p.val && root.val < q.val) {
    return root;
  } else if (p.val > root.val && q.val > root.val) {
    return lowestCommonAncestor(root.right, p, q);
  } else if (p.val < root.val && q.val < root.val) {
    return lowestCommonAncestor(root.left, p, q);
  }

  return root;
};

// or like this? ✅
var lowestCommonAncestor = function(root, p, q) {
  if (p.val > root.val && q.val > root.val) {
    return lowestCommonAncestor(root.right, p, q);
  } else if (p.val < root.val && q.val < root.val) {
    return lowestCommonAncestor(root.left, p, q);
  }
  return root;
};