# @param {Integer[]} nums
# @param {Integer} target
# @return {Integer[]}
def two_sum(nums, target)
    encountered = Hash.new

    nums.each_index { |i|
        complement = encountered.assoc(target - nums[i])

        if complement != nil then
            return [complement[1], i]
        else
            encountered[nums[i]] = i
        end
    }
end

RSpec.describe "two_sum from" do
    it "[2, 7, 11, 15] for 9 is [0, 1]" do
        expect(two_sum([2, 7, 11, 15], 9)).to eq([0, 1])
    end

    it "[3, 2, 4] for 6 is [1, 2]" do
        expect(two_sum([3, 2, 4], 6)).to eq([1, 2])
    end

    it "[3, 3] for 6 is [0, 1]" do
        expect(two_sum([3, 3], 6)).to eq([0, 1])
    end
end