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| -rw-r--r-- | challenge-139/jake/perl/ch-1.pl | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/challenge-139/jake/perl/ch-1.pl b/challenge-139/jake/perl/ch-1.pl new file mode 100644 index 0000000000..5118f4eb51 --- /dev/null +++ b/challenge-139/jake/perl/ch-1.pl @@ -0,0 +1,76 @@ +#!/r/bin/perl +use strict; +use warnings; + +# with this script, you can check whether an input list is sorted or not +# https://theweeklychallenge.org/blog/perl-weekly-challenge-139/#TASK1 + +### logic of the script +# +# the script will determine if a list is sorted by comparing each elements numeric difference to the first element in the list. +# an increasingly sorted list is characterized by a constant increase of each elements difference to the first element. +# a decreasingly sorted list is characterized by a constant decrease of each elements difference to the first element. +# constant differences are valid since list with duplicates are considered sorted, see 2. +# without warning upon other input. +# 1. if the input is only one element, the list is considered sorted and the script will exit. +# +# 2. subsequent diplicates are considered sorted. example lists +# (1,1,2) (1,2,2,3) +# input beginning with duplicates will be shifted until the list's first 2 elements are different from each other. +# this is necessary as the check_sorting subroutine is required to differentiate between increasing and decreasing lists. +# an initial difference (difference between 1st and 2nd element of input) of 0 does not provide the necessary positive or negative direction. +# +# 3. after the initial difference is determined, we know if the list must be checked against increase or decrease. +# sub check_sorting checks against several conditions while recursively chopping the list's head of. +# if we get to the last list element without violating the rule of constantly increasing / decreasing differences, we know the list is sorted or not. +# +### + +### limits of the script +# +# the script works only with ints without warning upon other input. +# +### + +# get input +print "input: "; +my @input_list = <STDIN>; +chomp @input_list; + +# if list has only 1 element it is considered sorted +my $list_length = @input_list; +if ( $list_length < 2) { + print "1\n"; + exit; +} + +# shift list if it begins with duplicates. +# this is necessary because the first difference in a list determines, if it is an increasing or decreasing list. +# the check_sorting subroutine depends on this discrimination +# if the first difference is 0, this discrimination cannot take place +my $initial_element = $input_list[0]; +while ( $list_length > 1 && $initial_element eq $input_list[1] ) { + shift ( @input_list ); +} + +my $initial_difference = $input_list[1] - $initial_element; +printf ( "%i\n", check_sorting ( $initial_element, @input_list, $initial_difference ) ); + +sub check_sorting { + my $length_leftover = @input_list; + # if there is only one element left in the list, and the subroutine is called again, the list is sorted + return 1 if ( $length_leftover < 2); + + # if the initial difference is negative, any subsequent difference must not be larger than that + if ( $initial_difference < 0 && $input_list[1] - $initial_element > $initial_difference ) { + return 0; + } + # if the initial difference is positive, any subsequent difference must not be smaller than that + if ( $initial_difference >= 0 && $input_list[1] - $initial_element < $initial_difference ) { + return 0; + } + else { + shift ( @input_list ); + check_sorting ( @input_list ); + } +}
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