Task — Check order

You are given an array of integers, @ints. Write a script to re-arrange the given array in an increasing order and return the indices where it differs from the original array.

Examples

Example 1
Input: @ints = (5, 2, 4, 3, 1)
Output: (0, 2, 3, 4)
Before: (5, 2, 4, 3, 1)
After : (1, 2, 3, 4, 5)
Difference at indices: (0, 2, 3, 4)

Example 2
Input: @ints = (1, 2, 1, 1, 3)
Output: (1, 3)
Before: (1, 2, 1, 1, 3)
After : (1, 1, 1, 2, 3)
Difference at indices: (1, 3)

Example 3
Input: @ints = (3, 1, 3, 2, 3)
Output: (0, 1, 3)
Before: (3, 1, 3, 2, 3)
After : (1, 2, 3, 3, 3)
Difference at indices: (0, 1, 3)

Analysis

I tried doing this using grep or map and while I'm sure it's possible, I find code hard to maintain when $_ and $_[0] are mixed in a single expression - and especially when $_[$_] makes an appearance.

So I've gone for a slightly more wordy approach, which still works in negligible time for an @ints with thousands of elements.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2025-02-03
use utf8;     # Week 307 - task 1 - Check order
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

check_order(5, 2, 4, 3, 1);
check_order(1, 2, 1, 1, 3);

my @ints;
push @ints, int(rand(10)) for 0 .. 49;
check_order(@ints);

sub check_order {
    
    my (@ints, @sorted, @different, $j);
    
    # sort the list
    @ints = @_;
    @sorted = sort {$a <=> $b} @ints;
    
    # find indices where original and sorted differ
    for $j (0 .. $#ints) {
        push @different, $j if $ints[$j] != $sorted[$j];
    }       
    
    say qq[\nInput:  \@ints =      (] . join(', ', @ints) . ')';
    say qq[        \@sorted =    (] . join(', ', @sorted) . ')';
    say qq[Output: \@different = (] . join(', ', @different) . ')';
}

Output

Input:  @ints =      (5, 2, 4, 3, 1)
        @sorted =    (1, 2, 3, 4, 5)
Output: @different = (0, 2, 3, 4)

Input:  @ints =      (1, 2, 1, 1, 3)
        @sorted =    (1, 1, 1, 2, 3)
Output: @different = (1, 3)

Input:  @ints =      (5, 6, 8, 2, 6, 7, 6, 4, 9, 9, 1, 8,
2, 7, 8, 6, 6, 5, 9, 7, 9, 5, 3, 4, 4, 6, 0, 5, 3, 1, 8,
8, 2, 8, 1, 1, 9, 0, 9, 7, 2, 4, 1, 3, 0, 6, 1, 2, 6, 3)
        @sorted =    (0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2,
2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6,
6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8,
9, 9, 9, 9, 9, 9)
Output: @different = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
40, 41, 42, 43, 44, 45, 46, 47, 48, 49)