day 4

Author: selfsimilar

4a.php

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+<?php
+
+/**
+--- Day 4: High-Entropy Passphrases ---
+
+A new system policy has been put in place that requires all accounts to use a passphrase instead of simply a password. A passphrase consists of a series of words (lowercase letters) separated by spaces.
+
+To ensure security, a valid passphrase must contain no duplicate words.
+
+For example:
+
+    aa bb cc dd ee is valid.
+    aa bb cc dd aa is not valid - the word aa appears more than once.
+    aa bb cc dd aaa is valid - aa and aaa count as different words.
+
+The system's full passphrase list is available as your puzzle input. How many passphrases are valid?
+*/
+
+$input = <<<INPUT
+aa bb cc dd
+aa bb cc dd aa
+aa bb cc dd aaa
+INPUT;
+
+$passphrases = explode("\n", $input);
+$valid = 0;
+foreach ($passphrases as $passphrase) {
+  $words = explode(' ', $passphrase);
+  $total = count($words);
+  $unique = count(array_unique($words));
+  if ($total == $unique) {
+    $valid++;
+  }
+}
+
+print $valid . "\n";

4b.php

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+<?php
+
+/**
+--- Day 4: High-Entropy Passphrases ---
+
+A new system policy has been put in place that requires all accounts to use a passphrase instead of simply a password. A passphrase consists of a series of words (lowercase letters) separated by spaces.
+
+To ensure security, a valid passphrase must contain no duplicate words.
+
+For example:
+
+    aa bb cc dd ee is valid.
+    aa bb cc dd aa is not valid - the word aa appears more than once.
+    aa bb cc dd aaa is valid - aa and aaa count as different words.
+
+The system's full passphrase list is available as your puzzle input. How many passphrases are valid?
+
+The first half of this puzzle is complete! It provides one gold star: *
+--- Part Two ---
+
+For added security, yet another system policy has been put in place. Now, a valid passphrase must contain no two words that are anagrams of each other - that is, a passphrase is invalid if any word's letters can be rearranged to form any other word in the passphrase.
+
+For example:
+
+    abcde fghij is a valid passphrase.
+    abcde xyz ecdab is not valid - the letters from the third word can be rearranged to form the first word.
+    a ab abc abd abf abj is a valid passphrase, because all letters need to be used when forming another word.
+    iiii oiii ooii oooi oooo is valid.
+    oiii ioii iioi iiio is not valid - any of these words can be rearranged to form any other word.
+
+Under this new system policy, how many passphrases are valid?
+
+*/
+
+$input = <<<INPUT
+abcde fghij
+abcde xyz ecdab
+a ab abc abd abf abj
+iiii oiii ooii oooi oooo
+oiii ioii iioi iiio
+INPUT;
+
+$passphrases = explode("\n", $input);
+$valid = 0;
+foreach ($passphrases as $passphrase) {
+  $invalid = FALSE;
+  $words = explode(' ', $passphrase);
+  for ($i = 0; $i < count($words); $i++) {
+    $iword = str_split($words[$i]);
+    sort($iword);
+    for ($j = $i + 1; $j < count($words); $j++) {
+      $jword = str_split($words[$j]);
+      sort($jword);
+      if ($iword == $jword) {
+        $invalid = TRUE;
+        break(2);
+      }
+    }
+  }
+  if (!$invalid) {
+    print $passphrase . "\n";
+    $valid++;
+  }
+}
+
+print $valid . "\n";