Explore Perl Learn Perl Part 2 Hash References Custom structures

Challenges

1. Count vowels in 'Linguam refrenans temperet ne litis horror insonet, visum fovendo'


print("\n");
print("-" x 35, "\n");
print("Challenge 1: count vowels\n");
print("-" x 35, "\n");
$str = "Linguam refrenans temperet ne litis\nhorror insonet, visum fovendo";
print("$str\n\n");
%vowel_count = ();

for ($i = 0; $i < length($str); $i++) {
    $char = lc( substr( $str, $i, 1 ) );
    $vowel_count{$char}++ if ( $char =~ /[aeiou]/ );
}

foreach $vowel (sort( keys(%vowel_count) )) {
    print("$vowel => $vowel_count{$vowel}\n");
}	
print("\n" . "-" x 35, "\n");

2. Average of each student's math scores ('Sebastian', scores 45, 60, 72; 'Daniel', scores 55, 65, 70; 'Florence', scores 71, 79, 78)


print("\n"); 
print("-" x 35, "\n");
print("Challenge 2: average of each student's math scores\n");
print("-" x 35, "\n");

@AoA = (
 ['Sebastian', 45, 60, 72],
 ['Daniel', 55, 65, 70],
 ['Florence', 71, 79, 78],
);

for($i = 0; $i < scalar(@AoA); $i++) {
 print("Average math score student " . $AoA[$i][0] . ": " . eval ( ($AoA[$i][1] + $AoA[$i][2] + $AoA[$i][3]) / (scalar(@{@AoA[$i]} -1)) )  . "\n");
} 
print("\n" . "-" x 35, "\n");

3. Which sentence has the maximum number of words? 'The sun is very bright.', 'There are only five students here today.', 'I’d love that.' , 'I would like to be there'


print("\n");
print("-" x 35, "\n");
print("Challenge 3: which sentence has the maximum number of words? 'The sun is very bright.', 'There are only five students here today.', 'I’d love that.' , 'I would like to be there\n");
print("-" x 35, "\n");

$array_no = -1;

sub find_max_words {
	
    ($list) = @_;
    $max_words = 0;

    foreach $sentence (@$list)
    {
        $sentence =~ s/\h+/ /g;
        @words  = split(/\s{1}/, $sentence);
        $count  = scalar(@words);

        if ($count > $max_words) {
          $max_words = $count;
          $array_no++;
        }  
    }
    return $max_words;
}

@s = ('The sun is very bright.', 'There are only five students here today.', 'I’d love that.' , 'I would like to be there');
print("Maximum number of words is " . find_max_words(\@s) . " in the sentence '" . $s[$array_no] . "'\n");
print("\n" . "-" x 35, "\n");

4. Typo-generator IV: wrong letter when typing 'Reinier'


print("\n");
print("-" x 35, "\n");
print("Challenge 4: typo-generator IV: wrong letter when typing 'Reinier'\n");
print("-" x 35, "\n");
$str = "Reinier";	

%HoA = ( 
           'R' => ['E','T','G','F','D'],
           'r' => ['e','t','g','f','d'],
           'e' => ['w','r','f','d','s'],
           'i' => ['u','o','l','k','j'],
           'n' => ['b','m','h','j','k']                 
      );

for ($i = 0; $i < length($str); $i++) {

 $char = substr($str, $i, 1);
 @replace = @{$HoA{$char}};  
 for ($y = 0; $y < scalar(@replace); $y++) 
 { 
     substr($str, $i, 1, @replace[$y]);
     print $str . "\n"; 
     $str = "Reinier";  
 } 
}
print("-" x 35, "\n");

5. Typo-generator V: extra letter when typing 'Reinier'


print("\n");
print("-" x 35, "\n");
print("Challenge 5: typo-generator V: extra letter when typing 'Reinier'\n");
print("-" x 35, "\n");
$str = "Reinier";	

%HoA = ( 
           'R' => ['E','T','G','F','D'],
           'r' => ['e','t','g','f','d'],
           'e' => ['w','r','f','d','s'],
           'i' => ['u','o','l','k','j'],
           'n' => ['b','m','h','j','k']                 
      );

for ($i = 0; $i < length($str); $i++) {

 $char = substr($str, $i, 1);
 @replace = @{$HoA{$char}};  
 for ($y = 0; $y < scalar(@replace); $y++) { 
  substr($str, $i, 0, @replace[$y]);
  print $str . "\n"; 
  $str = "Reinier";  
 } 

}
print("-" x 35, "\n");

'Typo-generator I-III' can be found at the end of Part 1.

6. Find the common numbers of two arrays, using a function and references


print("\n");
print("-" x 35, "\n");
print("Challenge 6: Find the common numbers of two arrays, using a function and references\n");
print("-" x 35, "\n");
sub intersection {
    ($f, $s) = @_;
    @result = ();
    foreach $item_1 (@$f) {
        foreach $item_2 (@$s) {

            if(defined($item_2) && $item_1 eq $item_2) {
			   push(@result, $item_2);
			   undef($item_2);
			   last;
            }	

        }	  
    }
    return @result;	 
}

@one = (1..10);
@two = (8..15);
intersection(\@one, \@two);
print("@result\n"); # 8 9 10
print("-" x 35, "\n");

7. Create @array_of_arrays and store references to @array1, @array2, and @array3 within it. Each array consists of three numbers. Print the third number of the second array.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 7: Create @array_of_arrays and store references to @array1, @array2, and @array3 within it. Each array consists of three numbers. Print the third number of the second array.\n");
print("-" x 35, "\n");
@array1 = (1, 2, 3);
@array2 = (4, 5, 6);
@array3 = (7, 8, 9);

@array_of_arrays = (\@array1, \@array2, \@array3);
print( $array_of_arrays[1][2] );
print("-" x 35, "\n");

8. Create an array and store references to two anonymous arrays within it. Each array consists of three names. Print the third name of the first array and print all names.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 8: Create @AoA and store references to two anonymous arrays within it. Each array consists of three names. Print the third name of the first array and print all names.\n");
print("-" x 35, "\n");
@AoA = (
          [ qw( Sebastian Daniel Florence ) ],
          [ qw( Kirsten Bibian Niki ) ],
       );

print("The name of my third child is: ");
print( $AoA[0]->[2] );
print("\n");

foreach $aoa_ref (@AoA) {
    print("The names of all my children are: ");
	print("$_ ") foreach (@$aoa_ref );
    print("\n");
}
print("-" x 35, "\n");

9. Store and print information about employees in a company. Each employee has a unique employee ID, and for each employee, we want to store their name, department, and salary. You should use a hash of hashes to represent this data structure.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 9: Store and print information about employees in a company. Each employee has a unique employee ID, and for each employee, we want to store their name, department, and salary. You should use a hash of hashes to represent this data structure.\n");
print("-" x 35, "\n");
%employees = ();

$employees{1001} = {
    name      => "John Doe",
    department => "Engineering",
    salary    => 60000
};

$employees{1002} = {
    name      => "Jane Smith",
    department => "Marketing",
    salary    => 55000
};

$employees{1003} = {
    name      => "Alice Johnson",
    department => "Human Resources",
    salary    => 50000
};

foreach $emp_id (keys %employees) {
    print "Employee ID: $emp_id\n";
    print "Name: " . $employees{$emp_id}{name} . "\n";
    print "Department: " . $employees{$emp_id}{department} . "\n";
    print "Salary: \$" . $employees{$emp_id}{salary} . "\n";
    print "\n";
}
print("-" x 35, "\n");

10. Store and print information about three books (title, author, genre, year of publication). Use push to add data for three books to the array of hashes.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 10: Store and print information about three books (title, author, genre, year of publication). Use push to add data for three books to the array of hashes.\n");
print("-" x 35, "\n");

@library = ();

push @library, {
    title       => "The Great Gatsby",
    author      => "F. Scott Fitzgerald",
    genre       => "Fiction",
    publication_year => 1925
};

push @library, {
    title       => "To Kill a Mockingbird",
    author      => "Harper Lee",
    genre       => "Fiction",
    publication_year => 1960
};

push @library, {
    title       => "1984",
    author      => "George Orwell",
    genre       => "Dystopian",
    publication_year => 1949
};

foreach $book (@library) {
    print "Title: " . $book->{title} . "\n";
    print "Author: " . $book->{author} . "\n";
    print "Genre: " . $book->{genre} . "\n";
    print "Publication Year: " . $book->{publication_year} . "\n";
    print "\n";
}
print("-" x 35, "\n");

11. Store and print information about students in a school. Each student has a name and a list of subjects they are studying. Use a hash of arrays.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 11: Store and print information about students in a school. Each student has a name and a list of subjects they are studying. Use a hash of arrays.\n");
print("-" x 35, "\n");
%students = ();

$students{"Alice"} = ["Math", "Physics", "Chemistry"];
$students{"Bob"} = ["English", "History"];
$students{"Charlie"} = ["Biology", "Geography", "Art"];
$students{"David"} = ["Computer Science"];

foreach $student (keys %students) {
    print "Student: $student\n";
    print "Subjects: " . join(", ", @{$students{$student}}) . "\n";
    print "\n";
}
print("-" x 35, "\n");

12. Read all lines under __DATA__ sequentially. All lines contains 3 semicolon separated integers. Use 'split' and 'push' to add them as references to anonymous arrays into @matrix. Print @matrix.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 12: Read all lines under __DATA__ sequentially. All lines contains 3 semicolon separated integers. Use 'split' and 'push' to add them as references to anonymous arrays into @matrix. Print @matrix.\n");
print("-" x 35, "\n");

@matrix = ();

@lines = <DATA>;
chomp(@lines);
foreach $line (@lines) {
    @split = split(';', $line);
    push @matrix, [ @split ];
}

foreach $AoA_ref (@matrix) {
    print("$_ ") foreach ( @$AoA_ref );
    print("\n");
}

__DATA__
1;2;3
4;5;6
7;8;9

print("-" x 35, "\n");

13. Print the length of a hash that has some key value pairs.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 13: Print the length of a hash that has some key value pairs.\n");
print("-" x 35, "\n");

%data = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
);

$length = keys %data;
print("$length\n");
print("-" x 35, "\n");

14. Add an element to the hash of the previous challenge and print the new length.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 14: Add an element to the hash of the previous challenge and print the new length.\n");
print("-" x 35, "\n");

%data = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
);

$data{'d'} = 4;
$length = keys %data;
print("$length\n");
print("-" x 35, "\n");

15. Remove the second element from the hash of the previous challenge and print the new length.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 15: Remove the second element from the hash of the previous challenge and print the new length.\n");
print("-" x 35, "\n");

%data = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
  'd' => 4,
);

delete $data{'b'};
$length = keys %data;
print("$length\n");

print("-" x 35, "\n");

16. Pass a hash to a function and print its keys and values in sorted order.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 16: Pass a hash to a function and print its keys and values in sorted order.\n");
print("-" x 35, "\n");

sub f {

    (%hash) = @_;
    foreach $item (sort keys(%hash)) {
      print("$item => $hash{$item}\n");
    }
}	

%data = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
  'd' => 4,
);

f(%data);
print("-" x 35, "\n");

17. Pass a hash as reference to a function and print its keys and values in sorted order.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 17: Pass a hash as reference to a function and print its keys and values in sorted order.\n");
print("-" x 35, "\n");

sub f {

    ($hash_ref) = @_;
    foreach $item (sort keys(%$hash_ref)) {
      print("$item => " . %{$hash_ref}{$item} . "\n");
    }
}	

%data = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
  'd' => 4,
);

f(\%data);
print("-" x 35, "\n");

18. Call a function by reference. Use the previous challenge.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 18: Call a function by reference. Use the previous challenge.\n");
print("-" x 35, "\n");

sub f {

    ($hash_ref) = @_;
    foreach $item (sort keys(%$hash_ref)) {
      print("$item => " . %{$hash_ref}{$item} . "\n");
    }
}	

%data = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
  'd' => 4,
);

$ref_f = \&f;
&$ref_f(\%data);

print("-" x 35, "\n");

19. Pass to a function: an integer, a reference to an array, a hash and a variable. Print their values.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 19: Pass to a function: an integer, a reference to an array, a hash, and a variable. Print their values.\n");
print("-" x 35, "\n");

sub f {

        for ( $i = 0; $i <= $#_; $i++ )  $#_ is the index of the last element in the array @_
        {			
           if (ref($_[$i]) eq "ARRAY") {
			       
              print("Argument nr. $i: @{$_[$i]} \n");				
			
           }				
           else {
				
              print("Argument nr. $i: " . $_[$i] ."\n");
			       
           }			       
        }	
}

$x = 14;
@array = qw( a b c );
%hash = ('a' => 1, 'b' => 2);
f ( 5, \@array, %hash, $x ); # Notice that passing the array (not as reference) would give the values a, b and c as separate results

print("-" x 35, "\n");

20. Pass to a function: an integer, an array, a reference to a hash and a variable. Print their values.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 20: Pass to a function: an integer, an array, a reference to a hash, and a variable. Print their values.\n");
print("-" x 35, "\n");

sub f {

        for ( $i = 0; $i <= $#_; $i++ )  $#_ is the index of the last element in the array @_
        {
			
            if (ref($_[$i]) eq "HASH") {
			       
              print("Argument nr. $i: @{[ (%{$_[$i]}) ]} \n");
              # [] creates reference to anonymous array; @{} dereferences this array; result: the hash is printed as a list!
			
            }				
            else {
				
              print("Argument nr. $i: " . $_[$i] ."\n");
			       
            }			       
        }	
}

$x = 14;
@array = qw( a b c );
%hash = ('a' => 1, 'b' => 2);
f ( 5, @array, \%hash, $x ); # See previous challenge for passing the hash not as reference

print("-" x 35, "\n");

21. Read three names: a first name and family name, separated by one space (e.g. Paul Auster). Print family name comma first name (e.g. Auster, Paul) in sorted order.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 21: Read three names: a first name and family name, separated by one space (e.g. Paul Auster). Print family name comma first name (e.g. Auster, Paul) in sorted order.\n");
print("-" x 35, "\n");

%names = ();
while (<DATA>) {
    chomp;
    ($fn, $ln) = split(' ', $_);
    $names{$ln} = $fn;
}

foreach $n ( sort( keys(%names) ) ) {
  print("$n, $names{$n}\n");
}

__DATA__
Umberto Eco
Albert Camus
Paul Auster

print("-" x 35, "\n");

22. Variant of challenge 21. Read three names: a first name, second name or initials (optional) and family name, separated by one space (e.g. Jean Paul Sartre). Print family name comma first name, second name/initial (e.g. Sarte, Jean Paul) in sorted order.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 22: Variant of challenge 21. Read three names: a first name, second name or initials (optional) and family name, separated by one space (e.g. Jean Paul Sartre). Print family name comma first name, second name/initial (e.g. Sarte, Jean Paul) in sorted order.\n");
print("-" x 35, "\n");
%names = ();
while (<DATA>) {
    chomp;
    @fn_ln = split(' ', $_);

    if (scalar(@fn_ln) == 2) { # e.g. Michel Foucault
		
       $fn = $fn_ln[0];
       $ln = $fn_ln[1];
       $names{$ln} = $fn;
	
    }
    else { # e.g. Jean Paul Sartre and Henry J. James

       $fn = $fn_ln[0] . " " . $fn_ln[1];
       $ln = $fn_ln[2];
       $names{$ln} = $fn;
    }	 
}

foreach $n (sort(keys(%names))) {
    print("$n, $names{$n}\n");
}

__DATA__
Michel Foucault
Jean Paul Sartre
Henry J. James

print("-" x 35, "\n");

23. Write a program that has to be invoked with one argument. The program converses a month to its corresponding number (1-12). Print the result.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 23: Write a program that has to be invoked with one argument. The program converses a month to its corresponding number (1-12). Print the result.\n");
print("-" x 35, "\n");

$USAGE = "month.pl name month"; # assume that this program is saved as month.pl

%months = (
    'January'   => 1,
    'February'  => 2,
    'March'     => 3,
    'April'     => 4,
    'May'       => 5,
    'June'      => 6,
    'July'      => 7,
    'August'    => 8,
    'September' => 9,
    'October'   => 10,
    'November'  => 11,
    'December'  => 12
);

$selected_month = "";

if (@ARGV != 1) { 
    die "Expected one argument: $USAGE";
}

if (@ARGV == 1) { 

        $selected_month = shift @ARGV;        
        $selected_month = ucfirst( lc( $selected_month ) ); # $selected_month should be capitalized
	    @mc_arg = (grep { $selected_month eq $_ } qw(January February March April May June July August September October November December));

		die "Error: expected the name of a month as argument!" if (! @mc_arg);
}

print("$selected_month has number $months{$selected_month}\n") if defined( $months{$selected_month} );

print("-" x 35, "\n");

24. Variant of challenge 23. Modify it with minimal changes. Write a program that has to be invoked with one argument. The program converses the number (1-12) to the correponding month name. Print the result.

	
print("\n");
print("-" x 35, "\n");
print("Challenge 24: Variant of challenge 23. Modify it with minimal changes. Write a program that has to be invoked with one argument. 
The program converses a number (1-12) to the correponding month name. Print the result.\n");
print("-" x 35, "\n");

$USAGE = "month.pl number_month (1-12)"; # assume that this program is saved as month.pl

%months = (
    'January'   => 1,
    'February'  => 2,
    'March'     => 3,
    'April'     => 4,
    'May'       => 5,
    'June'      => 6,
    'July'      => 7,
    'August'    => 8,
    'September' => 9,
    'October'   => 10,
    'November'  => 11,
    'December'  => 12
);

$selected_month_number = "";

if (@ARGV != 1) { 
    die "Expected one argument: $USAGE";
}

if (@ARGV == 1) { 

    $selected_month_number = shift @ARGV;
    @mc_arg = (grep { $selected_month_number == $_ } (1..12));
    
    die "Error: expected the number of a month as argument!" if (! @mc_arg);
}

%rev_months = reverse(%months); # this is the crux of this modification of challenge 23: simply reversing the old hash
print("The number $selected_month_number corresponds to $rev_months{$selected_month_number}\n") if defined( $rev_months{$selected_month_number} );

print("-" x 35, "\n");