Task — Consecutive arrays

You are given a sorted list of unique positive integers. Write a script to return list of arrays where the arrays are consecutive integers.

Examples

Example 1:
Input:  (1, 2, 3, 6, 7, 8, 9)
Output: ([1, 2, 3], [6, 7, 8, 9])

Example 2:
Input:  (11, 12, 14, 17, 18, 19)
Output: ([11, 12], [14], [17, 18, 19])

Example 3:
Input:  (2, 4, 6, 8)
Output: ([2], [4], [6], [8])

Example 4:
Input:  (1, 2, 3, 4, 5)
Output: ([1, 2, 3, 4, 5])

Analysis

The easiest way to do this is to pass through the input list, and:

• if the current element $n equals the previous one + 1, append , $n to the output string, or
• if not, append ], [$n to the output string

Finally, bracket the output string thus: ([$output])

Try it 

#!/usr/bin/perl
use strict;
use warnings;
use v5.26;   # week 131 task 1

consecutive_arrays(1, 2, 3, 6, 7, 8, 9);
consecutive_arrays(11, 12, 14, 17, 18, 19);
consecutive_arrays(2, 4, 6, 8);
consecutive_arrays(1, 2, 3, 4, 5);

sub consecutive_arrays {

    my ($prev, $output, $j);

    # loop over list
    $prev = -1;
    for $j (@_) {
        $output .= ($j == ($prev + 1)) ?   ", $j" : "], [$j";
        $prev = $j;
    }
    $output =~ s|...||;   # tidy the start of $output
    say qq{\nInput:  (} . join(', ', @_) . qq{)\nOutput: ($output])};
}

last updated 2026-03-09 — 8 lines of code

Output

Input:  (1, 2, 3, 6, 7, 8, 9)
Output: ([1, 2, 3], [6, 7, 8, 9])

Input:  (11, 12, 14, 17, 18, 19)
Output: ([11, 12], [14], [17, 18, 19])

Input:  (2, 4, 6, 8)
Output: ([2], [4], [6], [8])

Input:  (1, 2, 3, 4, 5)
Output: ([1, 2, 3, 4, 5])