add: 第一个只出现一次的字符

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] || ' '
+}