maximum_path_sum_i.rb

# https://projecteuler.net/problem=18

data = %(
  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
).strip.split("\n").map { |row| row.strip.split.map(&:to_i) }

results = {}

data.each_with_index do |row, i|
  row.each_with_index do |col, j|
    node = [i, j]
    results[node] ||= col
    previous_nodes = []
    previous_nodes << [i - 1, j] if i > 0 && j < row.size - 1
    previous_nodes << [i - 1, j - 1] if i > 0 && j > 0
    previous_nodes.each do |previous_node|
      tmp = results[previous_node] + col
      results[node] = tmp if tmp > results[node]
    end
  end
end

puts(results.values.max)