Add solution #137

Author: JoshCrozier

README.md

@@ -82,6 +82,7 @@
 134|[Gas Station](./0134-gas-station.js)|Medium|
 135|[Candy](./0135-candy.js)|Hard|
 136|[Single Number](./0136-single-number.js)|Easy|
+137|[Single Number II](./0137-single-number-ii.js)|Medium|
 141|[Linked List Cycle](./0141-linked-list-cycle.js)|Easy|
 142|[Linked List Cycle II](./0142-linked-list-cycle-ii.js)|Medium|
 143|[Reorder List](./0143-reorder-list.js)|Medium|

solutions/0137-single-number-ii.js

@@ -0,0 +1,26 @@
+/**
+ * 137. Single Number II
+ * https://leetcode.com/problems/single-number-ii/
+ * Difficulty: Medium
+ *
+ * Given an integer array nums where every element appears three times except for one, which appears
+ * exactly once. Find the single element and return it.
+ *
+ * You must implement a solution with a linear runtime complexity and use only constant extra space.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var singleNumber = function(nums) {
+  let a = 0, b = 0;
+
+  nums.forEach(c => {
+    const offset = (~a & b & c) | (a & ~b & ~c);
+    b = (~a & ~b & c) | (~a & b & ~c);
+    a = offset;
+  });
+
+  return a | b;
+};