aoc2016/php/bscott05.php

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2017-06-26 20:19:55 -05:00
<?php
set_time_limit(0);
/*
* Advent of Code 2016
* Day 5 (part 1 and 2)
*/
function calculateHashes($salt, $max = 8) {
$result = array();
$count = 0;
$start = 0;
$cache_file = md5($salt).".cache";
if(file_exists($cache_file)) {
$result = file($cache_file);
if(count($result) >= $max)
return $result;
}
for($i = 0; $i < 1000000000; $i++) {
$hash = md5($salt.$i);
if(substr($hash, 0, 5) === '00000') {
$result[$count++] = $hash;
if($count >= $max)
break;
}
}
file_put_contents($cache_file, implode("\n", $result));
return $result;
}
$puzzle_input = 'reyedfim';
$hashes = calculateHashes($puzzle_input, 30);
// Part 1
$password = '';
for($i = 0; $i < 8; $i++) {
$password .= substr($hashes[$i], 5, 1);
}
echo "Step 1 Password: $password\n";
// Part 2
$password = array_fill(0, 8, '_');
for($i = 0; $i < count($hashes); $i++) {
$pos = substr($hashes[$i], 5, 1);
$char = substr($hashes[$i], 6, 1);
if (is_numeric($pos) && (int)$pos < 8 && $password[(int)$pos] === '_')
$password[(int)$pos] = $char;
}
echo "Step 2 Password: ".implode($password);