122 lines
2.8 KiB
PHP
122 lines
2.8 KiB
PHP
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<?php
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$input_file = '../inputs/day3.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$binaries = array_map(fn ($str) => trim($str), explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($binaries) . "\n";
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print 'Part 2 answer: ' . solve_part_two($binaries) . "\n";
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}
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}
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function solve_part_one(array $binaries): int
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{
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$gamma = "";
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$epsilon = "";
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for ($i = 0; $i < strlen($binaries[0]) - 1; $i++) {
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$zeroes = 0;
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$ones = 0;
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foreach ($binaries as $bin) {
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if ((int)($bin[$i]) == 0)
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$zeroes += 1;
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else
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$ones += 1;
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}
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if ($zeroes > $ones) {
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$gamma .= "0";
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$epsilon .= "1";
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} else {
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$gamma .= "1";
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$epsilon .= "0";
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}
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}
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return bindec($gamma) * bindec($epsilon);
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}
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function solve_part_two(array $binaries): int
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{
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$o2 = "";
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$co2 = "";
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$possible_o2 = $binaries;
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$possible_co2 = $binaries;
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for ($i = 0; $i < strlen($possible_o2[0]); $i++) {
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$zeroes = 0;
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$ones = 0;
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foreach ($possible_o2 as $bin) {
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if ((int)($bin[$i]) == 0)
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$zeroes += 1;
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else
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$ones += 1;
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}
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if ($zeroes > $ones)
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$mcb = "0";
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elseif ($ones > $zeroes)
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$mcb = "1";
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else
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$mcb = "=";
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$new_o2 = [];
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foreach ($possible_o2 as $binary) {
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if ($o2 == "") {
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if ($mcb == "0" && $binary[$i] == "0")
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$new_o2[] = $binary;
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elseif (($mcb == "1" || $mcb == "=") && $binary[$i] == "1")
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$new_o2[] = $binary;
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}
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}
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if (count($new_o2) == 1)
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$o2 = $new_o2[0];
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else
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$possible_o2 = $new_o2;
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if ($o2 != "")
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break;
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}
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for ($i = 0; $i < strlen($possible_co2[0]); $i++) {
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$zeroes = 0;
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$ones = 0;
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foreach ($possible_co2 as $bin) {
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if ((int)($bin[$i]) == 0)
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$zeroes += 1;
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else
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$ones += 1;
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}
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if ($zeroes > $ones)
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$mcb = "0";
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elseif ($ones > $zeroes)
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$mcb = "1";
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else
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$mcb = "=";
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$new_co2 = [];
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foreach ($possible_co2 as $binary) {
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if ($co2 == "") {
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if (($mcb == "1" || $mcb == "=") && $binary[$i] == "0")
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$new_co2[] = $binary;
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elseif ($mcb == "0" && $binary[$i] == "1")
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$new_co2[] = $binary;
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}
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}
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if (count($new_co2) == 1)
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$co2 = $new_co2[0];
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else
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$possible_co2 = $new_co2;
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if ($co2 != "")
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break;
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}
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return bindec($o2) * bindec($co2);
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}
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