#235 - Lowest Common Ancestor of a Binary Search Tree

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Problem Description

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”

Solution

/**
 * 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 (p.val > root.val && q.val > root.val) {
    return lowestCommonAncestor(root.right, p, q);
  }
  if (p.val < root.val && q.val < root.val) {
    return lowestCommonAncestor(root.left, p , q);
  }
  return root;
};