add: 不同的二叉搜索树

.vscode/settings.json

@@ -36,5 +36,16 @@
     "zhan",
     "zhong",
     "zhuan"
-  ]
+  ],
+  "standard.options": {
+    "globals": [
+      "$",
+      "jQuery",
+      "fetch"
+    ],
+    "usePackageJson": true,
+    "env": {
+      "jest": true
+    }
+  }
 }

README.md

@@ -516,6 +516,10 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
   - LeetCode 108. 将有序数组转换为二叉搜索树 <https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/>
   - LintCode 106. 有序链表转换为二叉搜索树 <https://www.lintcode.com/problem/convert-sorted-list-to-binary-search-tree/description>
 
+- [不同的二叉搜索树](src/tree/unique-binary-search-trees.js)
+
+  - LeetCode 96. 不同的二叉搜索树 <https://leetcode-cn.com/problems/unique-binary-search-trees/>
+
 ## 链表
 
 - [合并 K 个排序链表](src/list/merge-k-sorted-lists.js)

src/tree/unique-binary-search-trees.js

@@ -0,0 +1,12 @@
+// 卡塔兰数
+/**
+ * @param {number} n
+ * @return {number}
+ */
+export const numTrees = function (n) {
+  let C = 1
+  for (let i = 0; i < n; ++i) {
+    C = C * 2 * (2 * i + 1) / (i + 2)
+  }
+  return C
+}

test/tree/unique-binary-search-trees.test.js

@@ -0,0 +1,5 @@
+import { numTrees } from '../../src/tree/unique-binary-search-trees'
+
+test('不同的二叉搜索树', () => {
+  expect(numTrees(3)).toBe(5)
+})