018.rb

triangle = <<END.split("\n").map { |line| line.split.map(&:to_i) }
75
95 64
17 47 82
18 35 87 10
20 04 82 47 65
19 01 23 75 03 34
88 02 77 73 07 63 67
99 65 04 28 06 16 70 92
41 41 26 56 83 40 80 70 33
41 48 72 33 47 32 37 16 94 29
53 71 44 65 25 43 91 52 97 51 14
70 11 33 28 77 73 17 78 39 68 17 57
91 71 52 38 17 14 91 43 58 50 27 29 48
63 66 04 68 89 53 67 30 73 16 69 87 40 31
04 62 98 27 23 09 70 98 73 93 38 53 60 04 23
END

table = Array.new(triangle.size) { Array.new(triangle.last.size, 0) }
table[0][0] = triangle[0][0]
1.upto(table.size - 1) do |r|
  triangle[r].size.times do |c|
    table[r][c] = triangle[r][c]
    if c > 0
      table[r][c] += [table[r-1][c], table[r-1][c-1]].max 
    else
      table[r][c] += table[r-1][c]
    end
  end
end
puts table.last.max