Project Euler Problems

17.rb

module Seventeen
  WORDS = {
    1000000 => "million",
    1000 => "thousand",
    100 => "hundred",
    90 => "ninety",
    80 => "eighty",
    70 => "seventy",
    60 => "sixty",
    50 => "fifty",
    40 => "forty",
    30 => "thirty",
    20 => "twenty",
    19=>"nineteen",
    18=>"eighteen",
    17=>"seventeen",
    16=>"sixteen",
    15=>"fifteen",
    14=>"fourteen",
    13=>"thirteen",
    12=>"twelve",
    11 => "eleven",
    10 => "ten",
    9 => "nine",
    8 => "eight",
    7 => "seven",
    6 => "six",
    5 => "five",
    4 => "four",
    3 => "three",
    2 => "two",
    1 => "one"
  }


  def self.num_to_words(number, join: " ")
    phrase = []
    remainder = number

    WORDS.each do |value, word|
      n = remainder / value

      if n > 0
        if n > 20
          count = self.num_to_words(n)
        else
          count = WORDS[n]
        end

        if phrase.last == "hundred"
          phrase.push("and")
        end

        unless n == 1 && value < 100
          phrase.push(count)
        end

        phrase.push(word)
      end
      remainder = remainder % value
    end
    phrase.join(join)
  end

  def self.range_sum(range)
    range.map {|n| self.num_to_words(n, join: "") }
  end

end

pp Seventeen::range_sum(1..1000).join('').length

18.rb

triangle_str  = <<TRIANGLE
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
TRIANGLE

triangle = triangle_str.split("\n").map do |l|
  l.split(" ").map do |s|
    s.to_i
  end
end

(triangle.length - 2).downto(0).each do |l|
  line = triangle[l]
  line.each_with_index do |cell, c|
    nextA = triangle[l + 1][c]
    nextB = triangle[l + 1][c + 1]
    triangle[l][c] = cell + [nextA, nextB].max
  end
end

puts triangle[0][0]

19.rb

def leap_year(y)
  if y % 400 == 0
    true
  elsif y % 100 == 0
    false
  elsif y % 4 == 0
    true
  else
    false
  end
end

def month_length(m, y)
  if m == 2
    if leap_year(y)
      29
    else
      28
    end
  elsif [4,6,9,11].include?(m)
    30
  else
    31
  end
end

weekday = 0
day = 1
month = 1
year = 1900
ml = month_length(month, year)
sundays = 0

loop do
  puts "#{year}, #{month}, #{day}, #{weekday}"

  if year >= 1901 && weekday == 6 && day == 1
    sundays += 1
  end

  break if year == 2000 && month == 12 && day == 31

  if day == ml
    day = 1
    if month == 12
      month = 1
      year +=1
    else
      month +=1
    end
    ml = month_length(month, year)
  else
    day += 1
  end

  weekday = (weekday + 1) % 7
end

pp sundays

20.rb

factorial = 1

(2..100).each do |n|
  factorial = factorial * n
end

digit_sum = 0

factorial.to_s.split('').each do |c|
  digit_sum += c.to_i
end

pp digit_sum

67.rb

# file from https://projecteuler.net/project/resources/p067_triangle.txt
triangle_str = File.open("p067_triangle.txt").read

triangle = triangle_str.split("\n").map do |l|
  l.split(" ").map do |s|
    s.to_i
  end
end

(triangle.length - 2).downto(0).each do |l|
  line = triangle[l]
  line.each_with_index do |cell, c|
    nextA = triangle[l + 1][c]
    nextB = triangle[l + 1][c + 1]
    triangle[l][c] = cell + [nextA, nextB].max
  end
end

puts triangle[0][0]