Source: https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/

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).”

/**
* 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}
*/
// O(H) time where H is height of tree, O(1) space
var lowestCommonAncestor = function(root, p, q) {
 const large = Math.max(p.val, q.val);
 const small = Math.min(p.val, q.val);
 
 let current = root;
 while (current !== null) {
   // If current root is greater than the larger node, the LCA must be in the left subtree
   if (current.val > large) {
     current = current.left;
   // If current root is less than the smaller node, the LCA must be in the right subtree
   } else if (current.val < small) {
     current = current.right;
   // small.val <= current.val <= large.val -> we found the LCA
   } else {
     return current;
   }
 } 
 
 return null;
};