Two Sum

Source: leetcode 1. Two Sum

Q. 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].

Answer

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
export default function twoSum (nums, target) {
  const seen = {}
  for (let i = 0; i < nums.length; i++) {
    const diff = target - nums[i]
    if (seen[diff] !== undefined) {
      return [seen[diff], i]
    } else {
      seen[nums[i]] = i
    }
  }
}