Euler 018 ruby Solution

Problem

By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum total from top to bottom is 23.

That is, 3 + 7 + 4 + 9 = 23.

Find the maximum total from top to bottom of the triangle below:

               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

NOTE: As there are only 16384 routes, it is possible to solve this problem by trying every route. However, Problem 67, is the same challenge with a triangle containing one-hundred rows; it cannot be solved by brute force, and requires a clever method!

Answer: 1074

Solution

euler018.rb

def maximum_path_sum_one(filename)
  rows = File.open(filename).map do |line|
    line.strip.split(',').map(&:to_i)
  end.reverse
  rows.each_with_index do |row, row_index|
    row.each_with_index do |val, val_index|
      next if val_index >= row.size - 1

      rows[row_index + 1][val_index] += [val, row[val_index + 1] || -1].max
    end
  end
  rows.last.first
rescue StandardError => e
  puts "***ERROR***: #{e}"
end

puts maximum_path_sum_one('./euler_18_data.txt') if __FILE__ == $PROGRAM_NAME

Euler 018 ruby Solution

Problem

Solution

See Also