1_two_sum.rb

# Leetcode Problem Url: https://leetcode.com/problems/two-sum/
# Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
#
#     You may assume that each input would have exactly one solution, and you may not use the same element twice.
#
#     You can return the answer in any order.
#
#
#
#     Example 1:
#
#     Input: nums = [2,7,11,15], target = 9
# Output: [0,1]
# Output: Because nums[0] + nums[1] == 9, we return [0, 1].
#
#     Example 2:
#
#     Input: nums = [3,2,4], target = 6
# Output: [1,2]
#
# Example 3:
#
#     Input: nums = [3,3], target = 6
# Output: [0,1]
#
#
#
# Constraints:
#
#     2 <= nums.length <= 105
# -109 <= nums[i] <= 109
# -109 <= target <= 109
# Only one valid answer exists.
#
# ----------------------------------------------------------------------------------------------------------------------
# @param {Integer[]} nums
# @param {Integer} target
# @return {Integer[]}
def two_sum(nums, target)
  data = {}

  nums.each_with_index do |num, index|
    data[num] = index
  end

  output = []

  nums.each_with_index do |num, index|
    expected_element = target - num

    if !data[expected_element].nil? && data[expected_element] != index
      output = [index, data[expected_element]]
      return output
    end
  end

  output

end

p two_sum([2, 7, 11, 15], 9)