How can I find the Nth largest value without using Perl's sort()?

Question

I have written following code in Perl:

#!/usr/bin/perl

@array = (3,6,8,1,2);

my $second_largest = 0;
my $largest = 0;

for (@array)
{
   if($_ > $largest)
   {
       $second_largest = $largest;
       $largest = $_;
   }
   if($_ > $second_largest && $_ < $largest)
   {
        $second_largest = $_;
   }
}
print "Second largest::".$second_largest;
print "largest::".$largest;

But I need a general code to find out "Nth" largest and smallest number of an array

Please help me

Answer 1

Just sort the array - the Nth largest will then be at the (SIZE - Nth) location.

Answer 2

use strict;
use warnings;
use Data::Dumper;
my @array=(1,2,10,0,20,45,12);
my @new=sort (@array);
print "The largest number is:$new[$#new]\n";
print "The second largest number is:$new[$#new-1]\n";

Answer 3

You need to look into the sort function. By creating a new array as the result of sorting your given one, you can then just use subscripting to get the Nth smallest and largest. Such as the code:

@array = (3,6,8,1,2);

@sorted = sort(@array);
print "@array " . "\n";
print "@sorted " . "\n";

print @sorted[1]  . "\n"; #  1 is the second smallest (since we're zero-based).
print @sorted[-2] . "\n"; # -2 is the second largest.

which outputs:

3 6 8 1 2
1 2 3 6 8
2
6

Be warned, if this is homework, you will almost certainly be caught for plagiarism if you use that code. This is a public forum that your educators will be able to see as well as you can. Read it, learn from it, write your own.

You may also want to add error checking code in case you try to find the 10th largest number in a seven-element array.

Answer 4

Most simple idea without using sort: for each element of the array: count the number of greater and smaller elements. If there are exactly N-1 greater elements, you have found your solution. And now do the rest of your homework by yourself, please.

Answer 5

You can use the following code also,

use strict;
use warnings;
use Data::Dumper;
use Sort::Array qw(Sort_Table);
my @array=(1,2,10,0,20,45,12);

my @new =Sort_Table(
    cols      => '1',
    field     => '1',
    sorting   => 'ascending',
    structure => 'csv',
    data      => \@array,
);

print "The largest number is:$new[$#new]\n";
print "The second largest number is:$new[$#new-1]\n";

Answer 6

Even though you say that you can't use Perl's sort, you can implement your own sort. Merge and quick sorts are well-known, explained in detail in many places, and really aren't a lot of code. Make friends with Google.

Once sorted, you merely go to the right array index.

If I were making this assignment to students, I'd give the highest marks to someone who:

• sorted the array
• maintained the sorted version
• allowed repeated inputs to select different values of N without re-sorting