Merge pull request youngyangyang04#867 from Tiffany-yuan/master

update: 0202.快乐数 js版本 使用Set()，求和用reduce

Author: youngyangyang04

problems/0202.快乐数.md

@@ -215,6 +215,23 @@ var isHappy = function(n) {
     }
     return n === 1;
 };
+
+// 方法四：使用Set()，求和用reduce
+var isHappy = function(n) {
+    let set = new Set();
+    let totalCount;
+    while(totalCount !== 1) {
+        let arr = (''+(totalCount || n)).split('');
+        totalCount = arr.reduce((total, num) => {
+            return total + num * num
+        }, 0)
+        if (set.has(totalCount)) {
+            return false;
+        }
+        set.add(totalCount);
+    }
+    return true;
+};
 ```
 
 Swift：