send+more=money

 1 require 'rubygems'
 2 require 'gecoder'
 3 
 4 # Solves the send+more=money problem: 
 5 # http://en.wikipedia.org/wiki/Send%2Bmore%3Dmoney
 6 solution = Gecode.solve do
 7   # A helper to make the linear equation a bit tidier. Takes a number of
 8   # variables and computes the linear combination as if the variable
 9   # were digits in a base 10 number. E.g. x,y,z becomes
10   # 100*x + 10*y + z .
11   def equation_row(*variables)
12     variables.inject{ |result, variable| variable + result*10 }
13   end
14 
15   # Set up the variables. 
16   # Let "letters" be an array of 8 integer variables with domain 0..9.
17   # The elements represents the letters s, e, n, d, m, o, r and y.
18   letters_is_an int_var_array(8, 0..9)
19   s,e,n,d,m,o,r,y = letters
20 
21   # Set up the constraints.
22   # The equation must hold.
23   (equation_row(s, e, n, d) + equation_row(m, o, r, e)).must ==
24     equation_row(m, o, n, e, y)
25 
26   # The initial letters may not be 0.
27   s.must_not == 0
28   m.must_not == 0
29 
30   # All letters must be assigned different digits.
31   letters.must_be.distinct
32 
33   # Tell Gecode what variables we want to know the values of.
34   branch_on letters, :variable => :smallest_size, :value => :min
35 end
36 
37 puts 's e n d m o r y'
38 puts solution.letters.values.join(' ')