gistfile1.rb

first_pass = {
  "A" => "1000000",
  "B" => "0100000",
  "C" => "0010000",
  "D" => "0001000",
  "E" => "0000100",
  "F" => "0000010",
  "G" => "0000001",
  "H" => "1100000",
  "I" => "1010000",
  "J" => "1001000",
  "K" => "1000100",
  "L" => "1000010",
  "M" => "1000001",
  "N" => "1110000",
  "O" => "1101000",
  "P" => "1100100",
  "Q" => "1100010",
  "R" => "1100001",
  "S" => "1111000",
  "T" => "1110100",
  "U" => "1110010",
  "V" => "1110001",
  "W" => "1111100",
  "X" => "1111010",
  "Y" => "1111001",
  "Z" => "1111100"
}

second_pass = {
  "A" => "1000011",
  "B" => "0100011",
  "C" => "0010011",
  "D" => "0001011",
  "E" => "0000111",
  "F" => "0000011",
  "G" => "0000011",
  "H" => "1100011",
  "I" => "1010011",
  "J" => "1001011",
  "K" => "1000111",
  "L" => "1000011",
  "M" => "1000011",
  "N" => "1110011",
  "O" => "1101011",
  "P" => "1100111",
  "Q" => "1100011",
  "R" => "1100011",
  "S" => "1111011",
  "T" => "1110111",
  "U" => "1110011",
  "V" => "1110011",
  "W" => "1111111",
  "X" => "1111011",
  "Y" => "1111011",
  "Z" => "1111111"
}

used_points = first_pass.values
second_pass.each_pair do |pair|
  puts "#{pair.first} code already used!" if used_points.include?(pair.last)
end

Here's a table of the results:

A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z
1	X							X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
2		X						X						X	X	X	X	X	X	X	X	X	X	X	X	X
3			X						X					X					X	X	X	X	X	X	X	X
4				X						X					X				X				X	X	X	X
5					X						X					X				X			X			X
6						X						X					X				X			X
7							X						X					X				X			X
1	X							X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
2		X						X						X	X	X	X	X	X	X	X	X	X	X	X	X
3			X						X					X					X	X	X	X	X	X	X	X
4				X						X					X				X				X	X	X	X
5					X						X					X				X			X			X
6	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
7	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X