first_sum_of_pairs.rb

# return the first pair starting from left whose sum is equal to given number
# sum_pairs([10, 5, 2, 3, 7, 5], 10) => [3,7]
# 				 ^-----------^
# 					   ^--^ #[3,7] came earlier than [5,5]

def sum_pairs(ints, sum)
    hash = {}

ints.each_with_index do |i,j|
	 if hash[i].nil? 
	 	hash[i]=[1,[j]]
	 else
	 	hash[i][0]+=1
	 	hash[i][1]<<j
	 end	
	 end
	 # print hash
	 # puts ""

min=10000000000
tuple=nil
ints.each do |i|
	if hash[sum-i].nil? || hash[i].nil?
		next
	elsif sum-i == i 
		if hash[i][0]>1 && min>hash[i][1][1]
			min = hash[i][1][1]	
			tuple = [i,i]
			hash[i]=nil
		end
	elsif min>hash[sum-i][1][0]
		min = hash[sum-i][1][0]
		tuple = [i,sum-i]
		hash[i]=nil
		hash[sum-i]=nil
	else
		hash[i]=nil
		hash[sum-i]=nil
	end	
	# print "#{min} #{tuple}\n"
end
tuple
end

print sum_pairs([1, 2, 3, 4, 1, 0], 2)
print sum_pairs([1, 2, 3, 4, 2, 5, 7, 6, 7], 9)
print sum_pairs([1, 2, 3, 4, 1, 4, 8, 9, 5], 8)


# 
# def sum_pairs(ints, s)
#   seen = {}
#   for i in ints do
#     return [s-i, i] if seen[s-i]
#     seen[i] = true
#   end
#   nil
# end
#