Addition: Two Sum problem

README.md

@@ -67,6 +67,7 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 - [Reverse String](src/_Problems_/reverse_string)
 - [Maximum Product of Three Numbers](src/_Problems_/max-product-of-3-numbers)
 - [Next Greater for Every Element in an Array](src/_Problems_/next-greater-element)
+- [Two Sum](src/_Problems_/two-sum)
 
 ### Searching
 

src/_Problems_/two-sum/index.js

@@ -0,0 +1,25 @@
+/*
+Two Sum Problem
+Given an array of integers, return indices of the two numbers such that they add up to a specific target.
+You may assume that each input would have exactly one solution, and you may not use the same element twice.
+
+Example:
+Given nums = [2, 7, 11, 15], target = 9,
+Because nums[0] + nums[1] = 2 + 7 = 9,
+return [0, 1].
+
+Solved in O(n) time complexity using Hash/Object
+*/
+
+function twoSum(nums, target) {
+    const numsHash = {};
+    for (let i = 0; i < nums.length; i++) {
+        const difference = target - nums[i];
+        if (numsHash[difference] !== undefined) {
+            return [numsHash[difference], i];
+        }
+        numsHash[nums[i]] = i;
+    }
+};
+
+module.exports = { twoSum };

src/_Problems_/two-sum/two-sum.test.js

@@ -0,0 +1,11 @@
+const { twoSum } = require('.');
+
+describe('Two Sum', () => {
+    it('Should return a index of elements added to get target', () => {
+        expect(twoSum([2, 7, 11, 15], 9)).toEqual([0, 1]);
+    });
+
+    it('Should return a index of elements added to get target', () => {
+        expect(twoSum([8, -4, 2, 14, 11, 17], 7)).toEqual([1, 4]);
+    });
+});