google sample interview ruby

=begin
For 2 arrays check if any pair
of numbers add up to 8
=end

#Questions
#Will I always expect numbers?
#Will the numbers always be integers? No foating numbers?
#Will the numbers all be positives?
#Is it all sorted?

#Assumptions
#Sorted and all positive integers 

def first_return8?(arr)
    #loop through the array and check each pairs
    arr.each.with_index do |a, i|
        new_arr = arr.select.with_index {|n, ind| ind != i }
        new_arr.each do |n|
            if a + n == 8
                return true
                break
            end
        end
    end
    return false
end

#puts first_return8?([1,2,3,4])

## first_return8? is bad. It has 0(N^2) and space complexity of O(N)


def second_return8?(arr, index_one = 0, index_two = arr.length-1)
    #we start from the lowest and move index2 back if pair sum is too high because index_two is 
    # always the highest value in the array.
    # We move the index1 up if pair sum is too low.
    # We must ensure the movement doesnt overlap, hence the unless statement
    unless index_one + 1 == index_two
        sum = arr[index_one] + arr[index_two]
        if sum == 8
            return true
        elsif sum < 8
            return second_return8?(arr, index_one + 1, index_two)
        else 
            return second_return8?(arr, index_one, index_two - 1)
        end
    end
    if arr[index_one] + arr[index_two] == 8 
        return true 
    end
    return false
end

puts second_return8?([1,2,4,5])