| 17 October 2025 | Challenge 340 |
Ascending Duplicates
Task 1: Duplicate Removals
Submitted by: Mohammad Sajid Anwar
You are given a string, $str, consisting of lowercase English letters.
Write a script to return the final string after all duplicate removals have been made. Repeat duplicate removals on the given string until we no longer can.
A duplicate removal consists of choosing two adjacent and equal letters and removing them.
Example 1
Input: $str = 'abbaca'
Output: 'ca'
Step 1: Remove 'bb' => 'aaca'
Step 2: Remove 'aa' => 'ca'
Example 2
Input: $str = 'azxxzy'
Output: 'ay'
Step 1: Remove 'xx' => 'azzy'
Step 2: Remove 'zz' => 'ay'
Example 3
Input: $str = 'aaaaaaaa'
Output: ''
Step 1: Remove 'aa' => 'aaaaaa'
Step 2: Remove 'aa' => 'aaaa'
Step 3: Remove 'aa' => 'aa'
Step 4: Remove 'aa' => ''
Example 4
Input: $str = 'aabccba'
Output: 'a'
Step 1: Remove 'aa' => 'bccba'
Step 2: Remove 'cc' => 'bba'
Step 3: Remove 'bb' => 'a'
Example 5
Input: $str = 'abcddcba'
Output: ''
Step 1: Remove 'dd' => 'abccba'
Step 2: Remove 'cc' => 'abba'
Step 3: Remove 'bb' => 'aa'
Step 4: Remove 'aa' => ''
Solution
This is another case for the s/// operator in an empty while loop.
use strict;
use warnings;
use experimental 'signatures';
sub duplicate_removals ($str) {
1 while $str =~ s/(.)\1//;
$str;
}
See the full solution to task 1.
Task 2: Ascending Numbers
Submitted by: Mohammad Sajid Anwar
You are given a string, $str, is a list of tokens separated by a single space. Every token is either a positive number consisting of digits 0-9 with no leading zeros, or a word consisting of lowercase English letters.
Write a script to check if all the numbers in the given string are strictly increasing from left to right.
Example 1
Input: $str = "The cat has 3 kittens 7 toys 10 beds"
Output: true
Numbers 3, 7, 10 - strictly increasing.
Example 2
Input: $str = 'Alice bought 5 apples 2 oranges 9 bananas'
Output: false
Example 3
Input: $str = 'I ran 1 mile 2 days 3 weeks 4 months'
Output: true
Example 4
Input: $str = 'Bob has 10 cars 10 bikes'
Output: false
Example 5
Input: $str = 'Zero is 0 one is 1 two is 2'
Output: true
Solution
Splitting the string at whitespace, selecting integers, sliding over pairs and check for strictly increasing values.
use strict;
use warnings;
use List::MoreUtils 'slideatatime';
sub ascending_numbers ($str) {
my $it = slideatatime 1, 2, grep /^\d+$/, split /\s+/, $str;
while (my @pair = $it->()) {
return if @pair > 1 && $pair[1] <= $pair[0];
}
1;
}
See the full solution to task 2.
If you have a question about this post or if you like to comment on it, feel free to open an issue in my github repository.