Merge pull request #44 from khairalanam/khair

Add Two Sum Problem

Author: devvsakib

L-I/0009 TwoSum/README.md

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+# 0009 TwoSum ( L-I )
+
+## Problem
+
+Given an array of integers `nums` and an integer `target`, return indices of the two numbers such that they add up to `target`.
+
+## Testcases
+
+- Input: `nums = [3, 2, 4], target = 6` <br>
+  Output: `[1, 2]`
+
+- Input: `nums = [2, 7, 11, 15], target = 9` <br>
+  Output: `[0, 1]`
+
+- Input: `nums = [3, 3], target = 6` <br>
+  Output: `[0, 1]`
+
+## Solution
+
+```javascript
+const TwoSum = (nums, target) => {
+  numToIndex = {};
+
+  for (let i = 0; i < nums.length; i++) {
+    if (target - nums[i] in numToIndex)
+      return [numToIndex[target - nums[i]], i];
+
+    numToIndex[nums[i]] = i;
+  }
+
+  return [];
+};
+```
+
+## How it works
+
+- The functiont takes an array of integers `nums` and an integer `target`.
+- We initialise an object `numToIndex` to push the element and its index as key-value pairs.
+- The function runs a for loop for the length of `nums`.
+- If the difference of `target` and the current element at `i`th index is present in the keys of `numToIndex`, then return the array that contains the element corresponding to the difference as well as the current element.
+- If not present, then set the element at `i`th index to be equal to `i` for `numToIndex`.
+- If the for loop terminates normally, then return an empty array.
+
+## References
+
+- [LeetCode](https://leetcode.com/problems/two-sum/)
+
+## Problem Added By
+
+- [GitHub](https://www.github.com/khairalanam)
+- [LinkedIn](https://www.linkedin.com/in/khair-alanam-b27b69221/)
+- [Twitter](https://twitter.com/khair_alanam)
+
+## Contributing
+
+Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

L-I/0009 TwoSum/TwoSum.js

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+const TwoSum = (nums, target) => {
+  numToIndex = {};
+
+  for (let i = 0; i < nums.length; i++) {
+    if (target - nums[i] in numToIndex)
+      return [numToIndex[target - nums[i]], i];
+
+    numToIndex[nums[i]] = i;
+  }
+
+  return [];
+};
+
+nums = [3, 2, 4];
+target = 6;
+
+nums1 = [2, 7, 11, 15];
+target1 = 9;
+
+nums2 = [3, 3];
+target2 = 6;
+
+console.log(TwoSum(nums, target));
+console.log(TwoSum(nums1, target1));
+console.log(TwoSum(nums2, target2));