236.js

/** ------------------------------------------------------------------------------
 * 
 * 236. Lowest Common Ancestor of a Binary Tree
 * Topics: Tree, Depth-First Search, Binary Tree
 * https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/
 * 
 ------------------------------------------------------------------------------ */
/**
 * 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 === p || root === q) return root

  const left = lowestCommonAncestor(root.left, p, q)
  const right = lowestCommonAncestor(root.right, p, q)

  if (left && right) return root
  return left || right
}

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