The weekly challenge 340 - Task 1: Duplicate Removals

 1 #!/usr/bin/env perl
 2 # https://theweeklychallenge.org/blog/perl-weekly-challenge-340/#TASK1
 3 #
 4 # Task 1: Duplicate Removals
 5 # ==========================
 6 #
 7 # You are given a string, $str, consisting of lowercase English letters.
 8 #
 9 # 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.
10 #
11 # # A duplicate removal consists of choosing two adjacent and equal letters and removing them.
12 #
13 ## Example 1
14 ##
15 ## Input: $str = 'abbaca'
16 ## Output: 'ca'
17 ##
18 ## Step 1: Remove 'bb' => 'aaca'
19 ## Step 2: Remove 'aa' => 'ca'
20 #
21 #
22 ## Example 2
23 ##
24 ## Input: $str = 'azxxzy'
25 ## Output: 'ay'
26 ##
27 ## Step 1: Remove 'xx' => 'azzy'
28 ## Step 2: Remove 'zz' => 'ay'
29 #
30 #
31 ## Example 3
32 ##
33 ## Input: $str = 'aaaaaaaa'
34 ## Output: ''
35 ##
36 ## Step 1: Remove 'aa' => 'aaaaaa'
37 ## Step 2: Remove 'aa' => 'aaaa'
38 ## Step 3: Remove 'aa' => 'aa'
39 ## Step 4: Remove 'aa' => ''
40 #
41 #
42 ## Example 4
43 ##
44 ## Input: $str = 'aabccba'
45 ## Output: 'a'
46 ##
47 ## Step 1: Remove 'aa' => 'bccba'
48 ## Step 2: Remove 'cc' => 'bba'
49 ## Step 3: Remove 'bb' => 'a'
50 #
51 #
52 ## Example 5
53 ##
54 ## Input: $str = 'abcddcba'
55 ## Output: ''
56 ##
57 ## Step 1: Remove 'dd' => 'abccba'
58 ## Step 2: Remove 'cc' => 'abba'
59 ## Step 3: Remove 'bb' => 'aa'
60 ## Step 4: Remove 'aa' => ''
61 #
62 ############################################################
63 ##
64 ## discussion
65 ##
66 ############################################################
67 #
68 # We can use a regular expression with backreference: Replace a single
69 # character followed by itself with an empty string while this still
70 # works.
71 
72 use v5.36;
73 
74 duplicate_removals('abbaca');
75 duplicate_removals('azxxzy');
76 duplicate_removals('aaaaaaaa');
77 duplicate_removals('aabccba');
78 duplicate_removals('abcddcba');
79 
80 sub duplicate_removals ($str) {
81     say "Input: $str";
82     while($str =~ s/(.)\1//) { }
83     say "Output: $str";
84 }