Submitted by: Mohammad S Anwar
You are given a positive integer, $n > 0.

Write a script to print the count of all special integers between 1 and $n.

An integer is special when all of its digits are unique.

Example 1:
Input: $n = 15
Output: 14 as except 11 all other integers between 1 and 15 are special.
Example 2:
Input: $n = 35
Output: 32 as except 11, 22, 33 all others are special.

perl -E 'say "$_->", 0+grep {!/^.*(\d).*\1.*$/} (1..$_) for(@ARGV);' 15 35 10000000

15->14
35->32
10000000->712890

perl -E 'say "$_->", 0+grep {!/^.*(\d).*\1.*$/} (1..$_) for(@ARGV);' 3748

3748->2109

 1  # Perl weekly challenge 195
 2  # Task 1:  Special Integers
 3  #
 4  # See https://wlmb.github.io/2022/12/12/PWC195/#task-1-special-integers
 5  use v5.36;
 6  use integer;
 7  use POSIX qw(lround);
 8  say(<<"FIN"), exit unless @ARGV;
 9  Usage: $0 N1 [N2...]
10  to get the number of special numbers between 1 and Ni
11  FIN
12  say "$_->", special($_) for @ARGV;
13  sub fact($n){ # factorial
14      my $r=1;
15      $r*=$_ for (1..$n);
16      $r
17  }
18  sub special($n){
19      my $k=0;
20      my $count=0;
21      while($k<=9 && 10**($k+1) < $n){
22          # Count from 1 to 9, then from 10 to 99, then from 100 to 999, etc.
23          $count += 9*fact(9)/fact(9-$k);
24          ++$k;
25      }
26      return $count if $k>9; # Nothing else to do eleven digit numbers or larger
27      #Count from 100.. to q00..-1
28      my $q=lround($n/10**$k);
29      $count += ($q-1)*fact(9)/fact(9-$k);
30      $count += final($q, $k-1, $n); # count from q00... upto $n=qxy...
31      return $count;
32  }
33  sub final($left, $power, $n){ # final approach from left 0 0 0 to n=x y z
34      my $count=0;
35      my $fixed=length $left; # leftward fixed digits
36      my %fixed;
37      ++$fixed{$_} for my @fixed=split '', $left; # actual fixed digits.
38      $_>1 && return 0 for(values %fixed); # nothing to add if fixed part is not special
39      return 1 if $power < 0; # Found last string
40      my $target=substr($n, $fixed, 1); # Next digit
41      for(0..$target-1){ # count upwards to target
42          next if $fixed{$_}; # skip seen digits
43          $count += fact(9-$fixed)/fact(9-$fixed-$power); # add rightwards contribution
44      }
45      $count += final($left.$target, $power-1, $n); # add digit to leftmost and recurse.
46      return $count;
47  }

./ch-1.pl 15 35 3748 10000000 1.0e9 1.0e10 1.0e11

15->14
35->32
3748->2109
10000000->712890

Submitted by: Mohammad S Anwar
You are given a list of numbers, @list.

Write a script to find most frequent even numbers in the list. In case you get more than
one even numbers then return the smallest even integer. For all other case, return -1.

Example 1
Input: @list = (1,1,2,6,2)
Output: 2 as there are only 2 even numbers 2 and 6 and of those 2 appears the most.
Example 2
Input: @list = (1,3,5,7)
Output: -1 since no even numbers found in the list
Example 3
Input: @list = (6,4,4,6,1)
Output: 4 since there are only two even numbers 4 and 6. They both appears the equal
number of times, so pick the smallest.

perl -E '$c{$_}++ for grep {!($_&1)} @ARGV; @e=sort {$c{$b} <=> $c{$a} || $a<=>$b} keys %c;
say join " ", @ARGV, " -> ", @e?shift @e:-1
' 1 1 2 6 2
perl -E '$c{$_}++ for grep {!($_&1)} @ARGV; @e=sort {$c{$b} <=> $c{$a} || $a<=>$b} keys %c;
say join " ", @ARGV, " -> ", @e?shift @e:-1
' 1 3 5 7
perl -E '$c{$_}++ for grep {!($_&1)} @ARGV; @e=sort {$c{$b} <=> $c{$a} || $a<=>$b} keys %c;
say join " ", @ARGV, " -> ", @e?shift @e:-1
' 6 4 4 6 1

1 1 2 6 2  ->  2
1 3 5 7  ->  -1
6 4 4 6 1  ->  4

1  # Perl weekly challenge 195
2  # Task 2:  Most Frequent Even
3  #
4  # See https://wlmb.github.io/2022/12/12/PWC195/#task-2-most-frequent-even
5  use v5.36;
6  my %count;
7  $count{$_}++ for grep {!($_&1)} @ARGV; # Filter evens and count them
8  my @sorted=sort {$count{$b} <=> $count{$a} || $a<=>$b} keys %count;
9  say join " ", @ARGV, " -> ", @sorted?shift @sorted:-1

./ch-2.pl 1 1 2 6 2
./ch-2.pl 1 3 5 7
./ch-2.pl 6 4 4 6 1

1 1 2 6 2  ->  2
1 3 5 7  ->  -1
6 4 4 6 1  ->  4