add: 快乐数

src/array/happy-number.js

@@ -0,0 +1,14 @@
+/**
+ * @param {number} n
+ * @return {boolean}
+ */
+export const isHappy = function (n) {
+  const set = new Set()
+
+  while (n !== 1 && !set.has(n)) {
+    set.add(n)
+    n = n.toString().split('').reduce((a, b) => a + b * b, 0)
+  }
+
+  return n === 1
+}