Project Euler — problem 17

August 8, 2012

(This article was first published on Tony's bubble universe » R, and kindly contributed to R-bloggers)

It has been two weeks since my last post on the 16th Euler problem. Now, since I just need a break after supper, I’m coming the 17th problem.

If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total. If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used? NOTE: Do not count spaces or hyphens.

This looks like a simple one, although patience and carefulness are required. For one-digit numbers, it’s one to nine; for two-digit numbers, it’s ten to nineteen for 10-19 and twenty to ninety-nine for 20-29; for three-digit numbers, it’s some hundred and two-digit numbers. Sounds a pattern, but I’ll sum the letters up simply arithmetically. So enough talking, here comes the solution, ugly but correctly…

^?View Code RSPLUS

nletter.single <- nchar(c("one", "two", "three", "four", "five", "six", "seven", "eight", "nine"))
nletter.teen <- nchar(c("ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "ninteen"))
nletter.ty <- nchar(c("twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninty"))
nletter.less100 <- sum(9 * nletter.single) + sum(nletter.teen) + sum(10 * nletter.ty)
nletter.hundreds <- sum(nletter.single) + 9 * nchar("hundred")
nletter.more100 <- 100 * nletter.hundreds + 99 * 9 * nchar("and") + 9 * nletter.less100
result <- nletter.less100 + nletter.more100 + nchar("onethousand")
cat("The result is:", result, "\n")

Meanwhile, I’m practising another language — perl. So I also came up with one perl script to convert number (1~999) to word. Just for fun!

^?View Code PERL

#!/usr/bin/perl
# number2word.pl by Tony Wei for covert numbers to words
use strict;
use warnings;
use Getopt::Long;
 
my $NUMBER;
 
my $opts = GetOptions(
        'number|i=i' => \$NUMBER,
        );
 
my %single_number = (
        '1' => 'one',
        '2' => 'two',
        '3' => 'three',
        '4' => 'four',
        '5' => 'five',
        '6' => 'six',
        '7' => 'seven',
        '8' => 'eight',
        '9' => 'nine',
);
 
my %teen_number = (
        '10' => 'ten',
        '11' => 'eleven',
        '12' => 'twelve',
        '13' => 'thirteen',
        '14' => 'fourteen',
        '15' => 'fifteen',
        '16' => 'sixteen',
        '17' => 'seventeen',
        '18' => 'eightteen',
        '19' => 'ninteen',
);
 
my %ty_number = (
        '2' => 'twenty',
        '3' => 'thirty',
        '4' => 'forty',
        '5' => 'fifty',
        '6' => 'sixty',
        '7' => 'seventy',
        '8' => 'eighty',
        '9' => 'ninty',
);
 
if ($NUMBER < 1 || $NUMBER > 999) {
        print "$NUMBER is beyond the range of 1~999.\n";
}
else {
        my $word;
        my @digits = split("", $NUMBER);
 
        if (scalar(@digits) == 1) {
                $word = $single_number{$NUMBER};
        }
        elsif (scalar(@digits) == 2) {
                if ($digits[0] == 1) {
                        $word = $teen_number{$NUMBER};
                }
                elsif ($digits[1] == 0) {
                        $word = $ty_number{$digits[0]};
                }
                else {
                        $word = $ty_number{$digits[0]}."_".$single_number{$digits[1]};
                }
        }
        else {
                if ($digits[1] == 0 && $digits[2] == 0) {
                        $word = $single_number{$digits[0]}." hundred";
                }
                else {
                        $word = $single_number{$digits[0]}." hundred and ";
                        if ($digits[1] == 0) {
                                $word = $word.$single_number{$digits[2]};
                        }
                        elsif ($digits[1] == 1) {
                                $word = $word.$teen_number{join("", @digits[1,2])};
                        }
                        elsif ($digits[2] == 0) {
                                $word = $word.$ty_number{$digits[1]};
                        }
                }
                else {
                        $word = $ty_number{$digits[0]}."-".$single_number{$digits[1]};
                }
        }
        else {
                if ($digits[1] == 0 && $digits[2] == 0) {
                        $word = $single_number{$digits[0]}." hundred";
                }
                else {
                        $word = $single_number{$digits[0]}." hundred and ";
                        if ($digits[1] == 0) {
                                $word = $word.$single_number{$digits[2]};
                        }
                        elsif ($digits[1] == 1) {
                                $word = $word.$teen_number{join("", @digits[1,2])};
                        }
                        elsif ($digits[2] == 0) {
                                $word = $word.$ty_number{$digits[1]};
                        }
                        else {
                                $word = $word.$ty_number{$digits[1]}."-".$single_number{$digits[2]};
                        }
                }
        }       
 
        print "The word for $NUMBER is '$word'.\n";
}