euler-4.rb

   1
   2 def is_palindrome?(n)
   3   n.to_s == n.to_s.reverse
   4 end
   5
   6
   7 a = b = limit = 999
   8
   9 directions = [:left, :back, :down, :forward]
  10
  11 direction = :left
  12
  13 puts "#{a}/#{b}, product = #{a*b}, dir = #{direction}"
  14
  15 while not is_palindrome?(a * b) do
  16   case direction
  17   when :left
  18     a -= 1
  19     direction = :back
  20   when :down
  21     b -= 1
  22     direction = :forward
  23   when :back
  24     if a < limit
  25       a += 1
  26     else
  27       direction = :forward
  28     end
  29     b -= 1
  30   when :forward
  31     if b < limit
  32       b += 1
  33     else
  34       direction = :back
  35     end
  36     a -= 1
  37   end
  38 # puts "#{a}/#{b}, product = #{a*b}, dir = #{direction}"
  39   end
  40
  41 if __FILE__==$0
  42   puts "Largest palindrome is #{a*b}, the product of #{a} and #{b}"
  43 end
  44
  45
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  47
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  49