82 lines
2.0 KiB
PHP
82 lines
2.0 KiB
PHP
<?php
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/*
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* Advent of Code 2016
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* Day 4 (part 1 and 2)
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*/
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function extractRoomInfo($input_line) {
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if(preg_match("/(\S+)-(\d+)\[([^\]]*)\]/", $input_line, $output_array)) {
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return array(
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'room_name' => $output_array[1],
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'sector_id' => $output_array[2],
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'checksum' => $output_array[3]
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);
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}
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return false;
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}
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function generateChecksum($room_name) {
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// calculate char occurrences
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$char_count_array = count_chars(str_replace('-', '', $room_name), 1);
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// sort by occurrence count
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arsort($char_count_array);
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// group chars into occurrence count
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$dedupe = array();
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foreach($char_count_array as $char => $occurrence) {
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$dedupe[$occurrence][] = $char;
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}
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// cross my fingers and hope this actually works
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$checksum = '';
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foreach($dedupe as $occurrence => $chars) {
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sort($chars);
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for($i = 0; $i < count($chars); $i++) {
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$checksum .= chr($chars[$i]);
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}
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}
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// cut off the excess and return
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return substr($checksum, 0, 5);
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}
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function decryptRoomName($name, $sector_id) {
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$key = $sector_id % 26; // this should work right?
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$a_start = ord('a');
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$output = '';
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for($i = 0; $i < strlen($name); $i++) {
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$a = ord(substr($name, $i, 1));
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if($a == ord('-'))
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$output .= ' ';
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else
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$output .= chr($a_start + ((($a - $a_start) + $key) % 26));
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}
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return $output;
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}
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$input = file('day4_input.txt');
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//$input = array("aaaaa-bbb-z-y-x-123[abxyz]", "a-b-c-d-e-f-g-h-987[abcde]", "not-a-real-room-404[oarel]");
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// Part 1
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$valid_room_sum = 0;
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$valid_rooms = array();
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foreach($input as $line) {
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$room_info = extractRoomInfo($line);
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$generated_checksum = generateChecksum($room_info['room_name']);
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if($generated_checksum == $room_info['checksum']) {
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$valid_rooms[] = $room_info;
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$valid_room_sum += (int)$room_info['sector_id'];
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}
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}
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echo "valid room sum: $valid_room_sum<br />\n";
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// Part 2
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foreach($valid_rooms as $room) {
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$decrypted_name = decryptRoomName($room['room_name'], (int)$room['sector_id']);
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echo "room name: $decrypted_name, sector: {$room['sector_id']}<br />\n";
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}
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