From 7069c6846f92986217ef33821740328381a309bd Mon Sep 17 00:00:00 2001
From: "E. Choroba" <choroba@matfyz.cz>
Date: Wed, 23 Sep 2020 00:31:38 +0200
Subject: Solve 079: Count Set Bits & Trapped Rain Water by E. Choroba

---
 challenge-079/e-choroba/perl/ch-1.pl | 69 ++++++++++++++++++++++++++++++++++++
 challenge-079/e-choroba/perl/ch-2.pl | 37 +++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100755 challenge-079/e-choroba/perl/ch-1.pl
 create mode 100755 challenge-079/e-choroba/perl/ch-2.pl

diff --git a/challenge-079/e-choroba/perl/ch-1.pl b/challenge-079/e-choroba/perl/ch-1.pl
new file mode 100755
index 0000000000..120f281102
--- /dev/null
+++ b/challenge-079/e-choroba/perl/ch-1.pl
@@ -0,0 +1,69 @@
+#!/usr/bin/perl
+use warnings;
+use strict;
+
+sub count_set_bits {
+    my ($n) = @_;
+    my ($nearest_power2) = int(log($n) / log(2));
+    my $s = ($nearest_power2 * 2 ** ($nearest_power2 - 1) + 1);
+    my $rest = $n - 2 ** $nearest_power2;
+    $s += $rest + count_set_bits($rest) if $rest > 0;
+    return int($s % 1000000007)
+}
+
+use Test::More;
+
+is count_set_bits(4), 5, 'Example 1';
+is count_set_bits(3), 4, 'Example 2';
+is count_set_bits(1000), 4938, 'Thousand';
+is count_set_bits(10_000), 64613, 'Ten thousand';
+is count_set_bits(2 ** 26 - 1), 872415232, 'Two to 26';
+is count_set_bits(2 ** 30), 106127249, 'Modulo hit';
+is count_set_bits(2 ** 32 - 1), 719476260, 'Max 32bit';
+is count_set_bits(2 ** 32), 719476261, 'Max 32bit + 1';
+
+# For 2 ** 48 and 2 ** 48 - 1, it returns the same numbers :-(
+is count_set_bits(2 ** 47 - 1), 953198898, 'Max correct - 1';
+is count_set_bits(2 ** 47), 953198899, 'Max correct';
+
+done_testing();
+
+__END__
+
+Explanation:
+e.g. N=11
+
+0001
+0010
+0011
+0100
+0101
+0110
+0111
+1000
+1001
+1010
+1011
+
+The nearset lower power of 2 is 8 = 2 ** 3. We can ignore the leading
+zeros in the first 7 lines, and add the 3 zeros from the eight line.
+We get all the possible binary numbers 0 .. 7, there are 12 zeros and
+12 ones, which is 3 * 2 ** (3 - 1):
+
+.001
+.010
+.011
+.100
+.101
+.110
+.111
+.000
+
+We can now add the leading 1 from the last line.
+
+The remaining numbers all start with a 1. We count the ones (3 here),
+remove them, and count the ones in the remaining lines by recursion:
+
+.001
+.010
+.011
diff --git a/challenge-079/e-choroba/perl/ch-2.pl b/challenge-079/e-choroba/perl/ch-2.pl
new file mode 100755
index 0000000000..fadbb0ef09
--- /dev/null
+++ b/challenge-079/e-choroba/perl/ch-2.pl
@@ -0,0 +1,37 @@
+#!/usr/bin/perl
+use warnings;
+use strict;
+
+sub trapped_rain_water {
+    my @n = @_;
+    my ($volume, $left, $i) = (0) x 3;
+    while (++$i <= $#n) {
+        if ($n[$left] <= $n[$i]) {
+            my $height = $n[$left] < $n[$i]
+                       ? $n[$left]
+                       : $n[$i];
+            $volume += $height - $n[$_] for $left + 1 .. $i - 1;
+            $left = $i;
+        }
+    }
+    $volume += trapped_rain_water(@n[reverse $left .. $#n])
+        if $n[$left] > $n[-1];
+    return $volume
+}
+
+use Test::More;
+
+is trapped_rain_water(2, 1, 4, 1, 2, 5), 6, 'Example 1';
+is trapped_rain_water(3, 1, 3, 1, 1, 5), 6, 'Example 2';
+is trapped_rain_water(reverse 2, 1, 4, 1, 2, 5), 6, 'Example 1 reversed';
+is trapped_rain_water(reverse 3, 1, 3, 1, 1, 5), 6, 'Example 2 reversed';
+
+is trapped_rain_water(1, 2, 3, 2, 1), 0, 'zero';
+
+is trapped_rain_water(3, 1, 1, 2), 2, 'simple';
+is trapped_rain_water(reverse 3, 1, 1, 2), 2, 'simple reversed';
+
+is trapped_rain_water(3, 1, 2, 1, 3, 1, 2, 1, 2), 7, 'long';
+is trapped_rain_water(reverse 3, 1, 2, 1, 3, 1, 2, 1, 2), 7, 'long reversed';
+
+done_testing();
-- 
cgit