Project Euler Problem #17

February 3, 2010

Read the details of the problem here

Summary

How many letters would be needed to write all the numbers in words from 1 to 1000?

Solution

This isn’t actually too bad to just solve on paper but, in the spirit of the problem, here’s a Groovy something that constructs a dictionary of the words up to one thousand omitting whitespace.

def words = [
    0:"", 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:"onethousand" ]

1.upto(999) {
  if (!words[it]) {
    if (it < 100) {
      words[it] = words[it.intdiv(10) * 10] + words[it % 10]
    }
    else {
      words[it] = "${words[it.intdiv(100)]}hundred"
      def r = it % 100
      if (r > 0) words[it] += "and${words[r]}"
    }
  }
}

def answer = words.values()*.size().sum()

A fun little problem to do. Note that, although the problem doesn’t need it, adding in a empty string for zero avoids some code that would otherwise have to deal with zero values. It runs in 0.69 seconds.

Conclusion

Quick and easy to write in Groovy. Wouldn’t actually be much much more complex or verbose to do in Java using the same algorithm. The Groovy listops made it easy to do the final summation of the word lengths.

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