Python で Project Euler #17「数字の文字数」

Problem 16 「数字の文字数」

1 から 5 までの数字を英単語で書けば one, two, three, four, five であり, 全部で 3 + 3 + 5 + 4 + 4 = 19 の文字が使われている.
では 1 から 1000 (one thousand) までの数字をすべて英単語で書けば, 全部で何文字になるか.
注: 空白文字やハイフンを数えないこと. 例えば, 342 (three hundred and forty-two) は 23 文字, 115 (one hundred and fifteen) は20文字と数える. なお, "and" を使用するのは英国の慣習.

Python

# n = 5
n = 1000

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

def number_to_word(num):
  if num in numbers:
    return numbers[num]
  elif num < 100:
    a = num % 10
    b = (num // 10) * 10
    return number_to_word(b) + "-" + number_to_word(a)
  else:
    a = num % 100
    b = num // 100
    if a == 0:
      return number_to_word(b) + " hundred"
    else:
      return number_to_word(b) + " hundred and " + number_to_word(a)

def to_character_num(word):
  return len(word.replace(" ", "").replace("-", ""))

seq = range(1, n+1)
words = map(number_to_word, seq)
result = sum(map(to_character_num, words))

print result
print result == 21124
print words[:6]
print words[-3:]

結果

21124
True
['one', 'two', 'three', 'four', 'five', 'six']
['nine hundred and ninety-eight', 'nine hundred and ninety-nine', 'one thousand']