Queue Enqueue/Dequeue

Algorithm

The replay uses the same three values in every language, so this Perl DSA implementation can be compared directly with the rest of the DSA track.

front The front is the oldest value still waiting in the queue.

FIFO A queue removes values in first-in, first-out order.

Visual walkthrough

The queue keeps the oldest value at the front and adds new values at the back.

Step 1 - Enqueue 10, 20, 30

New values join at the back. The oldest value, 10, stays at the front.

Step 2 - Dequeue removes 10

Removing from the front returns 10 and makes 20 the new front.

Basic Implementation

                            basic.pl
                        

                            use strict;
use warnings;

sub render { return join(" -> ", @_); }

my @queue;
push @queue, $_ for (10, 20, 30);
my @removed;
push @removed, shift @queue while @queue;
print render(@removed), "\n";

                        

Complexity

Time: O(1) per operation with a real queue
Space: O(n)

Implementation notes

my @queue declares the queue as a Perl array with the @ sigil.
The queue starts empty; the trace begins with [].
Enqueue uses push @queue, $_ for (10, 20, 30), appending each value to the back of the array.
After the enqueue step, the replayed queue is [10, 20, 30].
my @removed stores the values as they are dequeued.
Dequeue uses shift @queue, which removes and returns the front element of the Perl array.
push @removed, shift @queue while @queue repeats while the queue array is non-empty; in that condition, @queue is in scalar context and means length.
The first dequeue returns 10, leaving queue [20, 30] and removed [10].
The remaining dequeues return 20 and 30, leaving queue [] and removed [10, 20, 30].
render(@removed) receives the removed values as a list and joins them with " -> ".
print render(@removed), "\n" outputs 10 -> 20 -> 30.