Linked Structures

Delete by Value

Find the node before the target value and rewire its next pointer so the target node leaves the chain.

Algorithm

The replay labels nodes by value, such as node(20), and never exposes object identity or memory addresses. This Perl DSA implementation uses the same small chain as the rest of the DSA track.

predecessor Deletion needs the node before the one being removed.
rewiring The predecessor skips the target and points at the target's next node.

Basic Implementation

basic.pl
Replay: real traced execution (multi-file project)
use strict;
use warnings;

sub node {
    my ($value, $next) = @_;
    return { value => $value, next => $next };
}

sub render {
    my ($head) = @_;
    my @parts;
    my $cursor = $head;
    while (defined $cursor) {
        push @parts, $cursor->{value};
        $cursor = $cursor->{next};
    }
    return join(" -> ", @parts) . " -> null";
}

my $head = node(10, node(20, node(30, node(40, undef))));
my $target = 30;
my $cursor = $head;
while (defined $cursor->{next}) {
    if ($cursor->{next}->{value} == $target) {
        $cursor->{next} = $cursor->{next}->{next};
        last;
    }
    $cursor = $cursor->{next};
}
print render($head), "\n";

  1. head ← 10 -> 20 -> 30 -> 40 -> null, target ← 30

    1use strict;2use warnings;
    values this step10 -> 20 -> 30 -> 40 -> nullhead30target

  2. cursor ← node(20)

    12my $cursor = $head;13while (defined $cursor) {14    push @parts, $cursor->{value};
    values this stepnode(10) → node(20)cursor

  3. cursor.next ← node(40)

    1use strict;2use warnings;
    values this stepnode(30) → node(40)cursor.next

  4. stdout ← 10 -> 20 -> 40 -> null

    29}30print render($head), "\n";
    values this step10 -> 20 -> 40 -> nullstdout10 -> 20 -> 40 -> nullhead

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation notes

  • Keep the explicit node and pointer/reference operations; array shortcuts hide the linked-list state this lesson is meant to replay.
  • The final output prints the chain in a deterministic a -> b -> null form for cross-language comparison.