# RabbitFarm

### 2023-01-29

#### How Many Missing Coins?

*The examples used here are from the weekly challenge problem statement and demonstrate
the working solution.*

## Part 1

*You are given an array of unique numbers. Write a script to find out all missing numbers
in the range 0..$n where $n is the array size.*

### Solution

```
use v5.36;
use boolean;
sub missing_numbers{
my @numbers = @_;
my %h;
do { $h{$_} = undef } for @numbers;
my @missing = grep { !exists($h{$_}) } 0 .. @numbers;
return @missing;
}
MAIN:{
say q/(/ . join(q/, /, missing_numbers(0, 1, 3)) . q/)/;
say q/(/ . join(q/, /, missing_numbers(0, 1)) . q/)/;
say q/(/ . join(q/, /, missing_numbers(0, 1, 2, 2)) . q/)/;
}
```

### Sample Run

```
$ perl perl/ch-1.pl
(2)
(2)
(3, 4)
```

### Notes

This problem was a nice refresh on exists,
which is often confused with `defined`

. Here we want to see if the hash key *exists* at
all and so the use is appropriate. If we had wanted to see if the value keyed was defined,
well, that is the use for `defined`

!

## Part 2

*You are given an integer, $n > 0. Write a script to determine the number of ways of
putting $n pennies in a row of piles of ascending heights from left to right.*

### Solution

```
use v5.36;
use AI::Prolog;
use Hash::MultiKey;
MAIN:{
my $S = $ARGV[0];
my $C = "[" . $ARGV[1] . "]";
my $prolog = do{
local $/;
<DATA>;
};
$prolog =~ s/_COINS_/$C/g;
$prolog =~ s/_SUM_/$S/g;
$prolog = AI::Prolog->new($prolog);
$prolog->query("sum(Coins).");
my %h;
tie %h, "Hash::MultiKey";
while(my $result = $prolog->results){
my @s = sort @{$result->[1]};
$h{\@s} = undef;
}
for my $k ( sort { @{$b} <=> @{$a} } keys %h){
print "(" . join(",", @{$k}) . ")";
print "\n";
}
}
__DATA__
member(X,[X|_]).
member(X,[_|T]) :- member(X,T).
coins(_COINS_).
sum(Coins):-
sum([], Coins, 0).
sum(Coins, Coins, _SUM_).
sum(Partial, Coins, Sum):-
Sum < _SUM_,
coins(L),
member(X,L),
S is Sum + X,
sum([X | Partial], Coins, S).
```

### Sample Run

```
$ perl perl/ch-2.pl 5 1,2,3,4,5
(1,1,1,1,1)
(1,1,1,2)
(1,2,2)
(1,1,3)
(1,4)
(2,3)
(5)
```

### Notes

The approach here is the same that I used for the *Coins Sum* problem from
TWC 075. The only change is the added
sort by the length of the "piles".

## References

posted at: 18:30 by: Adam Russell | path: /perl | permanent link to this entry