PWC 227

PWC 227

Challenge 1 (Friday 13th)

This challenge requires us to count the number of times Friday 13th occurs in a particular year.

I use Date::Manip. This module probably has easier ways to do this using a Date Range, but my approach is easy enough. My &friday_13th subroutine takes the year as input, throws an exception if it is outside the specified range (1753 to 9999), and then cycles through the 13th of each month, counting the Fridays.

use Date::Manip;

my $dateobj=Date::Manip::Date->new();

sub friday_13th {
    my ($year)=@_;
    my $retval=0;
    ( ($year > 9999) || ($year < 1753) ) &&
        die "Year should be between 1753 and 9999";

    map {
        ( ($dateobj->new_date("$year-$_-13")->printf('%w') ) == 5 ) &&
            $retval++;
    }
    1 .. 12;
    
    $retval;
}  


Challenge 2 (Roman Maths)

This challenge requires us to implement a calculator that parses infix math operations using roman numerals. 

There are several CPAN modules that do this. I use Math::Roman, which is the most full-featured. It is somewhat more full-featured than the task specification, which requires returning a ``non potest'' for operations that the Romans didn't know how to do (like go beyond 3999 or calculate fractions or write zero as a numeral). 

My subroutine takes the infix expression as input, verifies that it is valid, then checks for various situations where a 'non potest' or 'nulla' (zero in Latin) is called for, and finally evals the expression and returns the output if it is less than 4000.

use Math::Roman qw(roman);

sub roman_maths {
    my ($string)=@_;
    
    ($string =~ /([IVXLCMD]+)\s*([+-\/\*]\**)\s*([IVXLCMD]+)/)
        || die 'Invalid input';
     
     
     ( ($2 eq '-') && ($1 eq $3) ) && return 'nulla';
     
     ( ($2 eq '-') && ( roman($1) < roman($3) ) ) &&
        return 'non potest';
     
     ( ($2 eq '/') && ( (roman($1) % roman($3) ) > 0 ) ) &&
        return 'non potest';
        
     my $roman=eval("roman($1) $2 roman($3)");
     if ($roman > 3999) {
        return 'non potest';
     }
     else {
        return $roman;
    }
}

I realized too late that my input validation regex is not foolproof. It allows the expression to contain gibberish operators like '+*' or '***'. Anyway, inputs like these will throw an error a few steps later, when the expression is eval'd, so รงa va enfin.

Comments

Post a Comment

Popular posts from this blog

PWC 258

PWC 258 Last week (#257) I finished challenge 2 and my blog post for challenge 257 late last week, so had only submitted challenge 1. Here is my blog post for PWC 257 , including the full code for my challenge 2 solution. This week, I have done both challenges in perl 4.019 on DOSBOX. Both scripts also work fine on the latest Perl 5.38. I also did the challenges in Raku, where they are one-liners.  Challenge 1 (Count Even Digits Number) We are given a list of integers, and asked to count the number of elements whose base-10 representation has an even number of digits. In Raku , this is a one-liner. Here it is: raku -e 'say +@*ARGS.grep({$_.chars %% 2})' $@ It could be a one-liner in Perl 4 too, but since I run it on DOSBOX, my script would not be a bash shell script. Here is the short subroutine that does the job.  sub count_even_digits {  scalar( grep( ((length($_) % 2) == 0), @_) ); } The full code is here . Challenge 2 (Sum of values) We are given an integer k  and a list in
Read more

PWC 249

PWC 249 Challenge 1 (Equal pairs) We are given a list of integers with an even number of elements. We are asked to check if the list can be completely divided into sub-lists of size 2 with each sub-list containing the same integer repeated, like say (2,2). If so, we are asked to return the list of such sub-lists. This is straightforward in Perl 5. I use modern conveniences this time, though it could be done using only primitive Perl 4 syntax. Here is my subroutine. It returns a list of array references. local *equal_pairs = sub {     #-- return () if input is of odd length     ((scalar(@_) % 2) > 0) && (return ());          #-- count number of occurrences of each element using a hash     local %_ = ();     map {$_{$_}++} @_;          #-- if any element occurs an odd number of times, return ()     (grep {($_{$_} % 2) > 0} keys %_) && (return ());          #-- loop thru %_ keys, returning pairs of such keys     map {         my $k=$_;         my $num_pairs=( ($_{$k}
Read more

PWC 253

PWC 253 I do both challenges this week using old software on DOSBOX: perl 4.019, and for comparison, also python 1.4 beta. My solutions also work on the current versions of Perl 5 (5.38) and Python 2 (2.7.18) respectively. Challenge 1 (Split Strings) Links to code: perl4.019 python1.4b We are given a list of strings, and a single character say sep . We are asked to return the list, with the strings split into component substrings using sep as a separator. We should not include any empty strings in the output. In perl 4, I first stick a backslash in front of the separator character, so that it is escaped if entered in a regex. This is because the perl split function takes a regex as its first argument indicating the separator. If we have a character like '$' or ',', we want to escape it so that it is read literally when parsing the regex. Here is the key subroutine:   sub split_strings {  local ($separator, @words)=@_;  local (@retval)=(); #array to be returned  #  #--
Read more