# Perl Weekly Challenge 187.

My solutions (task 1 and task 2 ) to the The Weekly Challenge - 187.

``````Submitted by: Mohammad S Anwar
Two friends, Foo and Bar gone on holidays seperately to the same city.
You are given their schedule i.e. start date and end date.

To keep the task simple, the date is in the form DD-MM and all dates belong to the
same calendar year i.e. between 01-01 and 31-12. Also the year is non-leap year
and both dates are inclusive.

Write a script to find out for the given schedule, how many days they spent
together in the city, if at all.

Example 1
Input: Foo => SD: '12-01' ED: '20-01'
Bar => SD: '15-01' ED: '18-01'

Output: 4 days
Example 2
Input: Foo => SD: '02-03' ED: '12-03'
Bar => SD: '13-03' ED: '14-03'

Output: 0 day
Example 3
Input: Foo => SD: '02-03' ED: '12-03'
Bar => SD: '11-03' ED: '15-03'

Output: 2 days
Example 4
Input: Foo => SD: '30-03' ED: '05-04'
Bar => SD: '28-03' ED: '02-04'

Output: 4 days
``````

Using the simplifications allowed by the task statement, I make a routine to convert from dates to 0-based day of the year. Then I subtract the smallest of the ending dates from the largest of the starting dates. If negative, there is no overlap. Otherwise, it is the off-by-one answer. This yelds the 2-liner

``````perl -MList::Util=sum,max,min -E '
@m=qw(31 28 31 30 31 30 31 31 30 31 30); sub d(\$x){(\$d,\$m)=split "-", \$x; \$d-1+sum @m[(0..\$m-2)]}
\$d=min(map {d(\$ARGV[\$_])}(1,3))-max(map {d(\$ARGV[\$_])}(0,2)); say \$d<0?0:\$d+1
' 12-01 20-01 15-01 18-01

perl -MList::Util=sum,max,min -E '
@m=qw(31 28 31 30 31 30 31 31 30 31 30); sub d(\$x){(\$d,\$m)=split "-", \$x; \$d-1+sum @m[(0..\$m-2)]}
\$d=min(map {d(\$ARGV[\$_])}(1,3))-max(map {d(\$ARGV[\$_])}(0,2)); say \$d<0?0:\$d+1
' 02-03 12-03 13-03 14-03

perl -MList::Util=sum,max,min -E '
@m=qw(31 28 31 30 31 30 31 31 30 31 30); sub d(\$x){(\$d,\$m)=split "-", \$x; \$d-1+sum @m[(0..\$m-2)]}
\$d=min(map {d(\$ARGV[\$_])}(1,3))-max(map {d(\$ARGV[\$_])}(0,2)); say \$d<0?0:\$d+1
' 02-03 12-03 11-03 15-03

perl -MList::Util=sum,max,min -E '
@m=qw(31 28 31 30 31 30 31 31 30 31 30); sub d(\$x){(\$d,\$m)=split "-", \$x; \$d-1+sum @m[(0..\$m-2)]}
\$d=min(map {d(\$ARGV[\$_])}(1,3))-max(map {d(\$ARGV[\$_])}(0,2)); say \$d<0?0:\$d+1
' 30-03 05-04 28-03 02-04
``````

Results:

``````4
0
2
4
``````

The full code is similar. I just add a few tests. A better code would use the package `DateTime` and friends, to allow for dates in different years and for leap years.

`````` 1  # Perl weekly challenge 187
2  # Task 1:  Days Together
3  #
5  use v5.36;
6  use List::Util qw(sum max min);
7  sub ddmm2days(\$x){
8      state @month_lengths=qw(31 28 31 30 31 30 31 31 30 31 30 31);
9      die "Wrong format: \$x" unless \$x=~/(\d\d)-(\d\d)/;
10      my (\$d,\$m)=(\$1, \$2);
11      die "Wrong month: \$m" unless 1<=\$m<=12;
12      die "Wrong day: \$d. Only \$month_lengths[\$m-1] days in month \$m"
13          unless 1<=\$d<=\$month_lengths[\$m-1];
14      \$d-1+sum @month_lengths[(0..\$m-2)]
15  }
16  die <<"FIN" unless @ARGV==4;
17  Usage: \$0 fs fe bs be
18  to obtain the number of days Foo and Bar are together,
19  where fs and fe are the start and end dates of Foo's holidays and
20  bs and be are the start and end dates of Bar's holidays. Dates are in the
21  format DD-MM.
22  FIN
23  my (\$foo_start, \$foo_end, \$bar_start, \$bar_end)=@ARGV;
24  my \$days=  min(map {ddmm2days(\$_)} (\$foo_end, \$bar_end))
25        - max(map {ddmm2days(\$_)}(\$foo_start, \$bar_start));
26  \$days=\$days<0?0:1+\$days;
27  say "Overlap between intervals (\$foo_start, \$foo_end) and (\$bar_start, \$bar_end) is \$days days";
``````

Examples:

``````./ch-1.pl 12-01 20-01 15-01 18-01
./ch-1.pl 02-03 12-03 13-03 14-03
./ch-1.pl 02-03 12-03 11-03 15-03
./ch-1.pl 30-03 05-04 28-03 02-04
``````

Results:

``````Overlap between intervals (12-01, 20-01) and (15-01, 18-01) is 4 days
Overlap between intervals (02-03, 12-03) and (13-03, 14-03) is 0 days
Overlap between intervals (02-03, 12-03) and (11-03, 15-03) is 2 days
Overlap between intervals (30-03, 05-04) and (28-03, 02-04) is 4 days
``````

``````Submitted by: Mohammad S Anwar
You are given a list of positive numbers, @n, having at least 3 numbers.

Write a script to find the triplets (a, b, c) from the given list that
satisfies the following rules.

1. a + b > c
2. b + c > a
3. a + c > b
4. a + b + c is maximum.
In case, you end up with more than one triplets having the maximum then
pick the triplet where a >= b >= c.

Example 1
Input: @n = (1, 2, 3, 2);
Output: (3, 2, 2)
Example 2
Input: @n = (1, 3, 2);
Output: ()
Example 3
Input: @n = (1, 1, 2, 3);
Output: ()
Example 4
Input: @n = (2, 4, 3);
Output: (4, 3, 2)
``````

I first sort the list in descending order. Then I use `combinations` from `Algorithm::Combinatorics` to produce all triplets (a,b,c). I choose the first (if any) that obeys b+c>a assuming that `combinations` returns combinations in order. As a>=b>=c, and all numbers are positive, this guarantees that a+b>c and a+c>b. The code fits a oneliner:

``````perl -MAlgorithm::Combinatorics=combinations -MList::Util=first -E '
@n=sort {\$b<=>\$a} @ARGV; say join " ", @\$_ for first {\$_->+\$_->>\$_->} combinations(\@n, 3)
' 1 2 3 2
``````

Results:

``````3 2 2

perl -MAlgorithm::Combinatorics=combinations -MList::Util=first -E '
@n=sort {\$b<=>\$a} @ARGV; say join " ", @\$_ for first {\$_->+\$_->>\$_->} combinations(\@n, 3)
' 1 3 2
``````

Results:

``````perl -MAlgorithm::Combinatorics=combinations -MList::Util=first -E '
@n=sort {\$b<=>\$a} @ARGV; say join " ", @\$_ for first {\$_->+\$_->>\$_->} combinations(\@n, 3)
' 4 3 2
``````

Results:

``````4 3 2
``````

I add a few checks to the full code. I use an iterator to avoid needlesly producing all triplets.

`````` 1  # Perl weekly challenge 187
2  # Task 2:  Magical Triplets
3  #
5  use v5.36;
6  use Algorithm::Combinatorics qw(combinations);
7  use List::Util qw(first);
8  die <<FIN unless @ARGV;
9  Usage: \$0 N1 N2 N3 [N4...]
10  to find the maximum ordered triplet with elements from {N1, N2...} that obeys
11  the strict triangle inequalities.
12  FIN
13  my @set = sort {\$b<=>\$a} @ARGV;
14  die "All numbers should be positive" unless \$set[-1]>0;
15  my \$iterator=combinations(\@set, 3);
16  while(my \$triplet=\$iterator->next){
17      die "Expected ordered triplet: \$triplet" # Currently uneeded
18          unless \$triplet->>=\$triplet->>=\$triplet->;
19      next unless \$triplet->+\$triplet->>\$triplet->;
20      say "Input: (", join(", ", @ARGV), ") Output: (", join(", ", @\$triplet), ")";
21      exit;
22  }
23  say "Input: (", join(", ", @ARGV), ") Output: ()";
``````

Examples:

``````./ch-2.pl 1 2 3 2
./ch-2.pl 1 3 2
./ch-2.pl 1 1 2 3
./ch-2.pl 2 4 3
#+end_example
``````

Results:

``````Input: (1, 2, 3, 2) Output: (3, 2, 2)
Input: (1, 3, 2) Output: ()
Input: (1, 1, 2, 3) Output: ()
Input: (2, 4, 3) Output: (4, 3, 2)
``````
Written on October 17, 2022