Peter
Peter Campbell Smith

Adopt a chilly ghost

Weekly challenge 215 — 1 May 2023

Week 215 - 1 May 2023

Task 2

Task — Number placement

You are given a list of numbers, all just 0 or 1. You are also given placement $count >=1.

Write a script to find out if it is possible to replace 0 with 1 in the given list $count times. The only condition is that you can only replace when there is no 1 on either side. Print 1 if it is possible, otherwise 0.

Analysis

The easiest way to do this - in my opinion - is to make the list into a string using join(). You can then try replacing a 0 with a 1 using s|||.

The examples all show replacing 000 with 010, but the rule implies that you can also replace an initial 00 with 10 or a final 00 with 01 so we'd better allow for that too.

The important line of code is:
$done ++ if ($string =~ s|000|010|
   or $string =~ s|^00|10| or $string =~ s|00$|01|);

which is executed $count times, and success is then given by $count == $done.

Try it 

Numbers (eg 1, 0, 0, 0, 1):

Count (eg 2):

Script


#!/usr/bin/perl

use v5.16;    # The Weekly Challenge - 2023-05-01
use utf8;     # Week 215 task 2 - Number placement
use strict;   # Peter Campbell Smith
use warnings; # Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

number_placement([1, 0, 0, 0, 1], 1);
number_placement([1, 0, 0, 0, 1], 2);
number_placement([0, 0, 1, 0, 0, 0, 1, 0, 0], 3);

sub number_placement {

    my (@numbers, $count, $string, $j, $done);
    
    @numbers = @{$_[0]};
    $count = $_[1];
    
    $string = join('', @numbers);
    for $j (1 .. $count) {
        $done ++ if ($string =~ s|000|010| or 
            $string =~ s|^00|10| or $string =~ s|00$|01|);
    }
    say qq[\nInput:  \@numbers = (] . join(', ', @numbers) .
        qq[), \$count = $count];
    say qq[Output: ] . ($done == $count ? 1 : 0);
    
}

Output


Input:  @numbers = (1, 0, 0, 0, 1), $count = 1
Output: 1

Input:  @numbers = (1, 0, 0, 0, 1), $count = 2
Output: 0

Input:  @numbers = (0, 0, 1, 0, 0, 0, 1, 0, 0), $count = 3
Output: 1

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