lowestCommonAncestorofaBinarySearchTree.js

////////////////////////////////////////////////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).”
// Example 1:
// Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
// Output: 6
// Explanation: The LCA of nodes 2 and 8 is 6.
// Example 2:
// Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
// Output: 2
// Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
// Example 3:
// Input: root = [2,1], p = 2, q = 1
// Output: 2
/**
 * 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}
 */
 const lowestCommonAncestor = function(root, p, q) {
    if (p.val < root.val && q.val < root.val) {
        return lowestCommonAncestor(root.left, p, q);
    }
    if (p.val > root.val && q.val > root.val) {
        return lowestCommonAncestor(root.right, p, q);
    }
    return root;
};

// console.log(lowestCommonAncestor([6,2,8,0,4,7,9,null,null,3,5], 2, 8));
// console.log(lowestCommonAncestor([6,2,8,0,4,7,9,null,null,3,5], 2, 4));
// console.log(lowestCommonAncestor([2,1], 2, 1));