Solution to task 1

1 files changed, 81 insertions, 0 deletions

diff --git a/challenge-205/jo-37/perl/ch-1.pl b/challenge-205/jo-37/perl/ch-1.pl
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+++ b/challenge-205/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0 '!float';
+use PDL;
+use PDL::NiceSlice;
+use List::Util 'uniqnum';
+
+our ($tests, $examples, $n);
+
+$n //= 3;
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [--] [N...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-n=N
+    find N-th largest element. Default: 3
+
+N...
+    list of integers
+
+EOS
+
+
+### Input and Output
+
+say nth_max($n, @ARGV);
+
+
+### Implementation
+
+# Keep N in the "N-th" largest element variable.
+
+sub nth_max {
+    my $n = shift;
+    # Not using PDL's "uniq" because it would sort the data.  There's a
+    # significant difference in running time for larger lists.
+	my $l = pdl uniqnum @_;
+    
+    # The "otherwise" branch: there is no n-th maximal element.
+    return max $l if $l->nelem < $n;
+
+    # Find the indices of the n largest elements.  Populates the second
+    # argument in its given size.
+    maximum_n_ind $l, my $max_ind = zeroes indx, $n;
+
+    # Pick the element indexed by the last in list, which is the n-th
+    # largest.
+    $l($max_ind(-1))->sclr;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is nth_max(3, (5, 3, 4)), 3, 'example 1';
+        is nth_max(3, (5, 6)), 6, 'example 2';
+        is nth_max(3, (5, 4, 4, 3)), 3, 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is nth_max(3, (3, 4, 3, 4, 3)), 4, 'not enought unique numbers';
+	}
+
+
+    done_testing;
+    exit;
+}