feat: add js solution to lc problem: No.0137

Author: rain84

solution/0100-0199/0137.Single Number II/README.md

@@ -359,6 +359,16 @@ function singleNumber(nums: number[]): number {
 }
 ```
 
+#### JavaScript
+
+```js
+function singleNumber(nums) {
+    const sumOfUnique = [...new Set(nums)].reduce((a, b) => a + b, 0);
+    const sum = nums.reduce((a, b) => a + b, 0);
+    return (sumOfUnique * 3 - sum) / 2;
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

solution/0100-0199/0137.Single Number II/README_EN.md

@@ -350,6 +350,16 @@ function singleNumber(nums: number[]): number {
 }
 ```
 
+#### JavaScript
+
+```js
+function singleNumber(nums) {
+    const sumOfUnique = [...new Set(nums)].reduce((a, b) => a + b, 0);
+    const sum = nums.reduce((a, b) => a + b, 0);
+    return (sumOfUnique * 3 - sum) / 2;
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

solution/0100-0199/0137.Single Number II/Solution3.js

@@ -0,0 +1,5 @@
+function singleNumber(nums) {
+    const sumOfUnique = [...new Set(nums)].reduce((a, b) => a + b, 0);
+    const sum = nums.reduce((a, b) => a + b, 0);
+    return (sumOfUnique * 3 - sum) / 2;
+}