add: 第一个只出现一次的字符

.vscode/settings.json

@@ -8,6 +8,7 @@
     "lcci",
     "lcof",
     "lcov",
+    "leetcode",
     "lrloseumgh",
     "mincost",
     "nums",

README.md

@@ -287,6 +287,12 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
 
   - LintCode 685. 数据流中第一个唯一的数字 <https://www.lintcode.com/problem/first-unique-number-in-data-stream/description>
 
+- [第一个只出现一次的字符](src/array/first-unique-character-in-a-string.js)
+
+  - LeetCode 面试题50. 第一个只出现一次的字符 <https://leetcode-cn.com/problems/di-yi-ge-zhi-chu-xian-yi-ci-de-zi-fu-lcof/>
+  - LeetCode 387. 字符串中的第一个唯一字符 <https://leetcode-cn.com/problems/first-unique-character-in-a-string/>
+  - LintCode 209. 第一个只出现一次的字符 <https://www.lintcode.com/problem/first-unique-character-in-a-string/description>
+
 ## 栈
 
 - [最大矩阵](src/stack/maximal-rectangle.js)

src/array/first-unique-character-in-a-string.js

@@ -0,0 +1,18 @@
+/**
+ * @param {string} s
+ * @return {character}
+ */
+export const firstUniqChar = function (s) {
+  const due = new Set()
+  const queue = new Set()
+  for (const n of s) {
+    if (queue.has(n)) {
+      queue.delete(n)
+      due.add(n)
+    } else if (!due.has(n)) {
+      queue.add(n)
+    }
+  }
+
+  return Array.from(queue)[0] || ' '
+}

test/array/first-unique-character-in-a-string.test.js

@@ -0,0 +1,5 @@
+import { firstUniqChar } from '../../src/array/first-unique-character-in-a-string'
+
+test('第一个只出现一次的字符', () => {
+  expect(firstUniqChar('leetcode')).toBe('l')
+})