After hearing about Ben’s motivation trouble with problem 17, I realized that I only had fun on that problem because I saw a rather fun algorithm. Since I’m rather proud of it, I’m going to show off the code here.

ones = ["", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"] tens = ["", "ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"] hundred = "hundred" and_ = "and" thousand = "thousand" sum = "" 1.upto(1000) do |i| curr = i out = "" if (curr > 999) then out += ones[curr/1000] + thousand curr = curr%1000 end if (curr > 99) then out += ones[curr/100] + hundred curr = curr%100 out += and_ if curr != 0 end if (curr >= 20) then out += tens[curr/10] curr = curr%10 out += ones[curr] else out += ones[curr] end sum += out end puts sum.length # Over 50 trials: # Mean: 17.3689 ms # Median: 16.5885 ms

I’m particularly proud of this code because I don’t have to convert the numbers into an array, and it’s blazing fast, even in ruby.