def two_sum(nums, target)
   #two sum really?
    # c = Hash.new do |h,k|
    #     p "h is #{h}, k is #{k}" 
    #     h[k] = []
    # end
    # c = Hash.new {|h,k| h[k] = [] }
    c = {}
    nums.each_with_index do |num, index|
        if !c[num]
            c[num] = [index]
        else
            c[num] << index
        end
    end
    
    c.each_pair do |k,v|
        if c[target - k]
            if k * 2 != target
                return [v.first, c[target - k].first]
            elsif k * 2 == target && v.length > 1
                return v
            end
        end
    end
end

[2,5,5,11]
10