B after A

You are given a string, $str. Write a script to return true if there is at least one b, and no a appears after the first b.

Examples

Example 1
Input: $str = "aabb"
Output: true

Example 2
Input: $str = "abab"
Output: false

Example 3
Input: $str = "aaa"
Output: false

Example 4
Input: $str = "bbb"
Output: true

Analysis

This is an easy one-liner:

($str =~ m|b(.*)| and $1 =~ m|^[^a]*$|) ? 
   'true' : 'false'

The first regular expression - $str =~ m|b(.*)| - looks for a 'b' and the second - $1 =~ m|^[^a]*$| - checks for no 'a' in the part of the string follwing the first 'b': note that the $1 refers to the matched substring from the first regular expression.

Perl pure regex implementation to deal with both tasks. Don't forget to try DIY tool.

This review may cover either or both challenges for this week.

Try it 

Try running the script with any input:

Your $str =

example: aardvarks live in burrows

⤡

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

use v5.26;    # The Weekly Challenge - 2024-06-10
use utf8;     # Week 273 - task 2 - B after a
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

b_after_a('aabb');
b_after_a('abab');
b_after_a('aaa');
b_after_a('bbb');
b_after_a('ccc');
b_after_a('Write a script to return true if there is at least one b');

sub b_after_a {
    
    my $str = $_[0];
    
    # match a 'b', and then match no 'a' in the rest of the string
    say qq[\nInput:  \$str = '$str'];
    say qq[Output: ] . (($str =~ m|b(.*)| and $1 =~ m|^[^a]*$|) ? 'true' : 'false');
}

4 lines of code

Output from script

Input:  $str = 'aabb'
Output: true

Input:  $str = 'abab'
Output: false

Input:  $str = 'aaa'
Output: false

Input:  $str = 'bbb'
Output: true

Input:  $str = 'ccc'
Output: false

Input:  $str = 'Write a script to return true if there 
   is at least one b'
Output: true