Weekly Challenge: Counting the XOR

Weekly Challenge 308

Each week Mohammad S. Anwar sends out The Weekly Challenge, a chance for all of us to come up with solutions to two weekly tasks. My solutions are written in Python first, and then converted to Perl. It's a great way for us all to practice some coding.

Challenge, My solutions

Task 1: Count Common

Task

You are given two array of strings, @str1 and @str2.

Write a script to return the count of common strings in both arrays.

My solution

The tasks and examples don't mention what to do if a string appears more than once in both arrays. I've made the assumption that we only need to return it once.

For the command line input, I take two strings that are space separated as shown in the example.

In Python this is a one liner. I turn the lists into sets (which only has unique values) and take the length of the intersection of these two sets.

def count_common(str1: list, str2: list) -> int:
    return len(set(str1) & set(str2))

Perl does not have sets or intersections built in. For the Perl solution, I turn both strings into a hash with the key being the strings. I then iterate through the keys of the first hash to see if they appear in the second hash. If they do, I increment the count variable.

sub main (@inputs) {
    my %str1 = map { $_, 1 } split( /\s+/, $inputs[0] );
    my %str2 = map { $_, 1 } split( /\s+/, $inputs[1] );

    my $count = 0;
    foreach my $str ( keys %str1 ) {
        $count++ if exists $str2{$str};
    }

    say $count;
}

Examples

$ ./ch-1.py "perl weekly challenge" "raku weekly challenge"
2

$ ./ch-1.py "perl raku java" "python java"
1

$ ./ch-1.py "guest contribution" "fun weekly challenge"
0

Task 2: Decode XOR

Task

You are given an encoded array and an initial integer.

Write a script to find the original array that produced the given encoded array. It was encoded such that encoded[i] = orig[i] XOR orig[i + 1].

My solution

This is relatively straight forward. For the command line input, I take the last value as the initial integer, and the rest as the encoded integers.

For this task, I create the orig list (array in Perl) with the initial value. I then iterate over each item in the encoded list and takes the exclusive-or of it and the last value in the orig list.

def decode_xor(encoded: list, initial: int) -> list:
    orig = [initial]

    for i in encoded:
        orig.append(i ^ orig[-1])

    return orig

Examples

$ ./ch-2.py 1 2 3 1
[1, 0, 2, 1]

$ ./ch-2.py 6 2 7 3 4
[4, 2, 0, 7, 4]

Comments

[henq_nl]

I prefer tools like map and grep to loops, b/c they are more concise.

my @str1 = qw ( perl weekly challenge perl);
my @str2 = qw ( raku challenge weekly raku);

@seen{@str1} = ();
@merged = (@str1, grep{!exists $seen{$_}} @str2);

print scalar @merged;
#6

#OR
my %saw;
my @out = grep( !$saw{$_}++, @str1, @str2);

print scalar @out;
#4