Add solution #236

Author: JoshCrozier

README.md

@@ -206,6 +206,7 @@
 232|[Implement Queue using Stacks](./0232-implement-queue-using-stacks.js)|Easy|
 234|[Palindrome Linked List](./0234-palindrome-linked-list.js)|Easy|
 235|[Lowest Common Ancestor of a Binary Search Tree](./0235-lowest-common-ancestor-of-a-binary-search-tree.js)|Easy|
+236|[Lowest Common Ancestor of a Binary Tree](./0236-lowest-common-ancestor-of-a-binary-tree.js)|Medium|
 237|[Delete Node in a Linked List](./0237-delete-node-in-a-linked-list.js)|Easy|
 238|[Product of Array Except Self](./0238-product-of-array-except-self.js)|Medium|
 242|[Valid Anagram](./0242-valid-anagram.js)|Easy|

solutions/0236-lowest-common-ancestor-of-a-binary-tree.js

@@ -0,0 +1,30 @@
+/**
+ * 236. Lowest Common Ancestor of a Binary Tree
+ * https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/
+ * Difficulty: Medium
+ *
+ * Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
+ *
+ * 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}
+ */
+var lowestCommonAncestor = function(root, p, q) {
+  if (!root || root === p || root === q) return root;
+  const [l, r] = [lowestCommonAncestor(root.left, p, q), lowestCommonAncestor(root.right, p, q)];
+  return l && r ? root : l ?? r;
+};