Task — Merging emails

You are given an array of accounts - names each with a list of email addresses.

Write a script to merge the accounts where possible. The accounts can be merged if they have at least one email address in common.

Analysis

My approach for this is to loop over the input accounts and:

• save each account name in an array $acct_name[$j],
• save every account's emails in a hash as $owns_email{$email} = $j provided that $email hasn't already been owned,
• and set $merge to point to its previous owner if it has been previously owned.

Once I've processed all the emails for each account, if $merge has been set, I go back and set the owner of all those emails to $merge.

So now every unique emaill address is in %owns_email, with a pointer to its new owner, or to its existing owner if it's not been merged.

And that's it, except that the second half of my script is devoted to printing the input and ouput in a pretty fashion that resembles Mohamammad's examples.

Try it 

#!/usr/bin/perl

# Peter Campbell Smith - 2023-03-20

use v5.28;
use utf8;
use warnings;

# You are given an array of accounts, ie name with list of email addresses.
# Write a script to merge the accounts where possible. The accounts can only 
# be merged if they have at least one email address in common.

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge/209/2

merge_accounts(['A', 'a1@a.com', 'a2@a.com'],
    ['B', 'b1@b.com'],
    ['A', 'a3@a.com', 'a1@a.com']);
merge_accounts(['A', 'a1@a.com', 'a2@a.com'],
    ['B', 'b1@b.com'],
    ['A', 'a3@a.com'],
    ['B', 'b2@b.com', 'b1@b.com']);
merge_accounts(['fred', 'fred@gmail.com', 'fgh@fgh.com', 'freddy@home.org'], 
    ['frederick', 'freddy@home.org'],
    ['fbloggs', 'fbloggs@bloggs.co.uk'],
    ['mary', 'freddy@home.org', 'mary@home.org']);

sub merge_accounts {
    
    my (@accounts, $a, $j, $k, @acct_name, @emails, $merge, %owns_emails, $email, $rubric, 
        $line, %lines, $owner, $rubric1);
    
    @accounts = @_;  # array of refs to accts
    
    # loop over accounts
    for $j (0 .. scalar @accounts - 1) {
        
        # loop over account details
        $merge = -1;  
        for $k (0 .. scalar @{$accounts[$j]} - 1) {

            # save account name and emails
            if ($k == 0) {
                $acct_name[$j] = $accounts[$j]->[0];
            } else {
                $email = $accounts[$j]->[$k];
                
                # mark for merging if email has been seen in a previous acct
                if (defined $owns_emails{$email}) {
                    $merge = $owns_emails{$email};
                
                # or record as seen here
                } else {
                    $owns_emails{$email} = $j;
                }
            }
        }
        
        # move emails from this account to $merge
        if ($merge >= 0) {
            for $email (keys %owns_emails) {
                if ($owns_emails{$email} == $j) {
                    $owns_emails{$email} = $merge;
                }
            }
        }           
    }
    
    # format input
    say qq{\nInput:  \@accounts = [};
    $rubric = $rubric1 = '';
    for $j (0 .. scalar @accounts - 1) {
        $rubric1 = '';
        for $k (0 .. scalar @{$accounts[$j]} - 1) {
            $rubric1 .=  qq{'$accounts[$j]->[$k]', };
        }
        $rubric1 =~ s|, $||;
        $rubric .= qq{   [$rubric1],\n};
    }
    $rubric =~ s|,\n$|]\n|;
    say qq{$rubric};
    
    # and output
    for $email (sort keys %owns_emails) {
        $owner = $owns_emails{$email};
        $lines{$owner} .= qq['$email', ];
    }
    
    $rubric = '';
    for $owner (sort keys %lines) {
        $lines{$owner} =~ s|, $|],|;
        $rubric .= qq{   ['$accounts[$owner]->[0]', $lines{$owner}\n};
    }
    $rubric =~ s|,\n$|]|;
    say qq{Output: \@accounts = [\n$rubric};
}

Output

Input:  @accounts = [
   ['A', 'a1@a.com', 'a2@a.com'],
   ['B', 'b1@b.com'],
   ['A', 'a3@a.com', 'a1@a.com']]

Output: @accounts = [
   ['A', 'a1@a.com', 'a2@a.com', 'a3@a.com'],
   ['B', 'b1@b.com']]

Input:  @accounts = [
   ['A', 'a1@a.com', 'a2@a.com'],
   ['B', 'b1@b.com'],
   ['A', 'a3@a.com'],
   ['B', 'b2@b.com', 'b1@b.com']]

Output: @accounts = [
   ['A', 'a1@a.com', 'a2@a.com'],
   ['B', 'b1@b.com', 'b2@b.com'],
   ['A', 'a3@a.com']]

Input:  @accounts = [
   ['fred', 'fred@gmail.com', 'fgh@fgh.com', 'freddy@home.org'],
   ['frederick', 'freddy@home.org'],
   ['fbloggs', 'fbloggs@bloggs.co.uk'],
   ['mary', 'freddy@home.org', 'mary@home.org']]

Output: @accounts = [
   ['fred', 'fgh@fgh.com', 'fred@gmail.com', 'freddy@home.org', 'mary@home.org'],
   ['fbloggs', 'fbloggs@bloggs.co.uk']]