From 64941ec53845cd72f6646df1e4dfda2037c267a5 Mon Sep 17 00:00:00 2001
From: yige <a@wyr.me>
Date: Sun, 10 May 2020 15:30:48 +0800
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---
 README.md                                     |  5 +++++
 ...lowest-common-ancestor-of-a-binary-tree.js | 20 +++++++++++++++++++
 ...t-common-ancestor-of-a-binary-tree.test.js |  8 ++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 src/tree/lowest-common-ancestor-of-a-binary-tree.js
 create mode 100644 test/tree/lowest-common-ancestor-of-a-binary-tree.test.js

diff --git a/README.md b/README.md
index 07c1b10..8ab20ce 100644
--- a/README.md
+++ b/README.md
@@ -305,6 +305,11 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
   - LeetCode 98. 验证二叉搜索树 https://leetcode-cn.com/problems/validate-binary-search-tree/
   - LintCode 95. 验证二叉查找树 https://www.lintcode.com/problem/validate-binary-search-tree/
 
+- [二叉树的最近公共祖先](src/tree/lowest-common-ancestor-of-a-binary-tree.js)
+
+  - LeetCode 236. 二叉树的最近公共祖先 https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/
+  - LintCode 88. 最近公共祖先 https://www.lintcode.com/problem/lowest-common-ancestor-of-a-binary-tree/description
+
 ## 链表
 
 - [合并K个排序链表](src/list/merge-k-sorted-lists.js)
diff --git a/src/tree/lowest-common-ancestor-of-a-binary-tree.js b/src/tree/lowest-common-ancestor-of-a-binary-tree.js
new file mode 100644
index 0000000..2014c09
--- /dev/null
+++ b/src/tree/lowest-common-ancestor-of-a-binary-tree.js
@@ -0,0 +1,20 @@
+/**
+ * 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}
+ */
+export const lowestCommonAncestor = function (root, p, q) {
+  if (!root || root === p || root === q) return root
+  const left = lowestCommonAncestor(root.left, p, q)
+  const right = lowestCommonAncestor(root.right, p, q)
+  if ((left === p && right === q) || (left === q && right === p)) return root
+  return left || right
+}
diff --git a/test/tree/lowest-common-ancestor-of-a-binary-tree.test.js b/test/tree/lowest-common-ancestor-of-a-binary-tree.test.js
new file mode 100644
index 0000000..b7a62d3
--- /dev/null
+++ b/test/tree/lowest-common-ancestor-of-a-binary-tree.test.js
@@ -0,0 +1,8 @@
+import { lowestCommonAncestor } from '../../src/tree/lowest-common-ancestor-of-a-binary-tree'
+import Tree from './Tree'
+
+test('二叉树的最近公共祖先', () => {
+  const head = Tree.arrToTree([3, 5, 1, 6, 2, 0, 8, null, null, 7, 4])
+  expect(lowestCommonAncestor(head, head.left, head.right)).toEqual(head)
+  expect(lowestCommonAncestor(head, head.left, head.left.right.right)).toEqual(head.left)
+})