Solution to task 1

1 files changed, 82 insertions, 0 deletions

diff --git a/challenge-236/jo-37/perl/ch-1.pl b/challenge-236/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0;
+use List::Util qw(min);
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [B...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+B...
+   list $5, $10 and $20 bills
+EOS
+
+
+### Input and Output
+
+say sell_juice(@ARGV) ? 'true' : 'false';
+
+
+### Implementation
+
+sub sell_juice {
+    # At the beginning, the trays for $5, $10 and $20 bills in our cash
+    # register are empty. Counting $20 bills, but never return them.
+    (\my %register)->@{5, 10, 20} = (0, 0, 0);
+    state $price = 5;
+
+    # Try to sell a juice for every given bill.
+    for my $bill (@_) {
+        # The amount to be returned.
+        my $return = $bill - $price;
+        # There is only one case, where the action is not uniquely
+        # defined: If we are to return $15, have three or more $5 bills
+        # and one or more $10 bills.  In this situation we give one $10
+        # bill and one $5 bill.
+        for my $tray (10, 5) {
+            my $cnt = min $register{$tray}, int $return / $tray;
+            # Take the bill(s) from the tray and adjust the to be
+            # returned amount.
+            $register{$tray} -= $cnt;
+            $return -= $cnt * $tray;
+        }
+        # Put the received bill into its tray.
+        $register{$bill}++;
+        # Fail if we cannot return the exact change.
+        return if $return;
+    }
+    # Here we succeeded.
+    1;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        ok  sell_juice(5, 5, 5, 10, 20), 'example 1';
+        ok !sell_juice(5, 5, 10, 10, 20), 'example 2';
+        ok  sell_juice(5, 5, 5, 20), 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        ok sell_juice(5, 5, 5, 5, 10, 20, 10), 'prefer 1x10 + 1x5 over 3x5';
+	}
+
+    done_testing;
+    exit;
+}