Add LeetCode-1 twoSum

Author: Soloydenko-C

__tests__/1-two-sum.ts

@@ -0,0 +1,15 @@
+import twoSum from '../src/leet-code/1-easy/1-two-sum';
+
+describe(twoSum.name, () => {
+  [
+    { nums: [1, 2], target: 3, expected: [0, 1] },
+    { nums: [1, 2, 3], target: 4, expected: [0, 2] },
+    { nums: [1, 2, 3], target: 5, expected: [1, 2] },
+    { nums: [1, 2, 3], target: 3, expected: [0, 1] },
+    { nums: [3, 3], target: 6, expected: [0, 1] },
+  ].forEach(({ nums, target, expected}) => {
+    it(`should return ${JSON.stringify({ expected })} for ${JSON.stringify({ nums })} and ${JSON.stringify({ target })}`, () => {
+      expect(twoSum(nums, target)).toEqual(expected);
+    });
+  });
+});

src/leet-code/1-easy/1-two-sum.ts

@@ -0,0 +1,50 @@
+/**
+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].
+```
+ */
+
+var twoSum = function(nums: number[], target: number): number[] {
+  const valuesAndIndices = nums.reduce((subResult, value, index) => {
+    const indices = subResult[value];
+    indices ? indices.push(index) : subResult[value] = [index];
+    return subResult;
+  }, { } as { [_: string]: number[] });
+
+  const sortedNums = [...nums].sort((a, b) => a - b);
+    
+  const restoreOriginalIndex = (indexInSorted: number): number => valuesAndIndices[sortedNums[indexInSorted].toString()].shift() as number;
+
+  let left = 0;
+  let right = left + 1;
+  while (true) {
+    const sum = sortedNums[left] + sortedNums[right];
+    if (sum === target) {
+      return [ restoreOriginalIndex(left), restoreOriginalIndex(right) ];
+    } else if (sum < target && right + 1 < sortedNums.length) {
+      right += 1;
+    } else {
+      left += 1;
+      right = left + 1;
+    }
+  }
+}
+
+var twoSumBruteForce = function(nums: number[], target: number): number[] {
+  for (let left = 0; left < nums.length - 1; left++)
+    for (let right = left + 1; right < nums.length; right++)
+      if (nums[left] + nums[right] === target)
+        return [left, right];
+  throw new Error(`Cheaters!`);
+};
+
+export default twoSum;