euler18.rb

   1 require 'logger'
   2
   3 $triangle_source = <<TRIANGLE
   4 75
   5 95 64
   6 17 47 82
   7 18 35 87 10
   8 20 04 82 47 65
   9 19 01 23 75 03 34
  10 88 02 77 73 07 63 67
  11 99 65 04 28 06 16 70 92
  12 41 41 26 56 83 40 80 70 33
  13 41 48 72 33 47 32 37 16 94 29
  14 53 71 44 65 25 43 91 52 97 51 14
  15 70 11 33 28 77 73 17 78 39 68 17 57
  16 91 71 52 38 17 14 91 43 58 50 27 29 48
  17 63 66 04 68 89 53 67 30 73 16 69 87 40 31
  18 04 62 98 27 23 09 70 98 73 93 38 53 60 04 23
  19 TRIANGLE
  20
  21 $triangle = $triangle_source.split("\n").map {|line| line.split.map {|s| s.to_i}}
  22
  23 def find_best(triangle)
  24   log = Logger.new(STDERR)
  25   log.level = Logger::WARN
  26   last_line_totals = [0]
  27   this_line_totals = []
  28   triangle.each do |line|
  29     log.info {"Checking line #{line}"}
  30     this_line_totals = []
  31     line.each_index do |i|
  32       this_line_totals << [i == 0 ? 0 : last_line_totals[i-1] + line[i],
  33                            i == last_line_totals.length ? 0 : last_line_totals[i] + line[i]].max
  34     end
  35     log.info {"Best totals for line #{line} are #{this_line_totals}"}
  36     last_line_totals = this_line_totals
  37   end
  38   log.close
  39   this_line_totals.max
  40 end
  41
  42 if __FILE__==$0
  43   puts find_best $triangle
  44 end