Missing numbers and

piles of pennies

Weekly challenge 201 — 23 January 2023

Week 201 - 23 Jan 2023

Task 1

We are given an array of unique numbers and asked to write a script to find out all missing numbers in the range 0..$n where $n is the array size.

The first thing to note is that there will always be at least one missing number, as there are $n + 1 numbers in the range 0 .. $n and only $n entries in the array.

The easy way to do this task is to convert the array to a string:

$string = ',' . join(',', @$array) . ',';

The string will look something like this:

,1,2,3,4,5,6,

Now all we have to do is to loop $j over 0 to $n - 1 and:

$result .= qq[$j, ] unless $string =~ m|,$j,|;

and with a little tidying up of the format, we have the result requested.

#!/usr/bin/perl # Peter Campbell Smith - 2023-01-23 # PWC 201 task 1 use v5.28; use utf8; use warnings; # Task: You are given an array of unique numbers. Write a script to find out all missing numbers in the range # 0..$n where $n is the array size. # Blog: https://pjcs-pwc.blogspot.com/2023/01/201-missing-numbers-and-piles-of-pennies.html my (@tests, $test, $string, $j, $result); @tests = ([0, 1, 3], [0, 1], [4, 5, 6], [6, 5, 4, 2, 1, 0], [0], []); # loop over tests for $test (@tests) { # make a string from the array $result = ''; $string = ',' . join(',', @$test) . ','; # $string = ,1,2,3, # check for missing numbers for $j (0 .. scalar @$test) { $result .= qq[$j, ] unless $string =~ m|,$j,|; } # report result $string =~ s|,|, |g; say qq[\nInput: \$array = (] . substr($string, 2, -2) . ')'; say qq[Output: ] . substr($result, 0, -2); }

Input: $array = (0, 1, 3) Output: 2 Input: $array = (0, 1) Output: 2 Input: $array = (4, 5, 6) Output: 0, 1, 2, 3 Input: $array = (6, 5, 4, 2, 1, 0) Output: 3 Input: $array = (0) Output: 1 Input: $array = () Output: 0

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Peter Campbell Smith is hereby placed in the public domain