155 lines
4 KiB
PHP
155 lines
4 KiB
PHP
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<?php
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$input_file = '../inputs/day16.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$lines = array_map('trim', explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($lines) . "\n";
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print 'Part 2 answer: ' . solve_part_two($lines) . "\n";
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}
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}
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function solve_part_one(array $lines): int
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{
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[$rules,, $nearby_tickets] = parse_lines($lines);
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$invalid_values = [];
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foreach ($nearby_tickets as $ticket) {
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foreach ($ticket as $field) {
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if (field_is_valid($rules, $field) == false)
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$invalid_values[] = $field;
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}
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}
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return array_sum($invalid_values);
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}
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function solve_part_two(array $lines): int
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{
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[$rules, $my_ticket, $nearby_tickets] = parse_lines($lines);
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$invalid_tickets = get_invalid_tickets($nearby_tickets, $rules);
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$valid_rules = get_valid_rules($rules, $my_ticket, $nearby_tickets, $invalid_tickets);
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$accum = 1;
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foreach ($valid_rules as $rule_name => $idx) {
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if (str_starts_with($rule_name, "departure"))
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$accum *= $my_ticket[$idx];
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}
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return $accum;
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}
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function get_valid_rules(array $rules, array $my_ticket, array $nearby_tickets, array $invalid_tickets): array
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{
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$possible_valid_rules = [];
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foreach ($rules as $rule) {
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for ($i = 0; $i < count($my_ticket); $i++) {
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$rule_valid = true;
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foreach ($nearby_tickets as $idx => $ticket) {
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if (in_array($idx, $invalid_tickets) == false) {
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$field = $ticket[$i];
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if ((($field >= $rule[1][0] && $field <= $rule[1][1]) || ($field >= $rule[2][0] && $field <= $rule[2][1])) == false) {
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$rule_valid = false;
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break;
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}
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}
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if ($rule_valid == false)
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break;
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}
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if ($rule_valid) {
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$possible_valid_rules[$i][] = $rule[0];
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}
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}
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}
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return get_valid_rules_from_possibilities($possible_valid_rules);
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}
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function get_valid_rules_from_possibilities(array $possible_valid_rules): array
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{
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$valid_rules = [];
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uasort($possible_valid_rules, fn ($x, $y) => count($x) > count($y) ? 1 : (count($x) < count($y) ? -1 : 0));
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for ($idx = 0; $idx < count($possible_valid_rules); $idx++) {
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$elem = $possible_valid_rules[array_keys($possible_valid_rules)[$idx]];
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if (count($elem) == 1) {
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$rule_name = $elem[array_keys($elem)[0]];
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$valid_rules[$rule_name] = $idx;
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$possible_valid_rules = array_map(fn ($arr) => array_diff($arr, $elem), $possible_valid_rules);
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}
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}
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return $valid_rules;
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}
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function get_invalid_tickets(array $nearby_tickets, array $rules): array
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{
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$invalid_tickets = [];
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foreach ($nearby_tickets as $idx => $ticket) {
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$ticket_valid = true;
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foreach ($ticket as $field) {
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if (field_is_valid($rules, $field) == false)
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$ticket_valid = false;
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}
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if ($ticket_valid == false)
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$invalid_tickets[] = $idx;
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}
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return $invalid_tickets;
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}
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function field_is_valid(array $rules, int $field): bool
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{
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$valid = false;
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foreach ($rules as $rule) {
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if (($field >= $rule[1][0] && $field <= $rule[1][1]) || ($field >= $rule[2][0] && $field <= $rule[2][1])) {
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$valid = true;
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break;
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}
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}
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return $valid;
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}
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function parse_lines(array $lines): array
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{
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$section = 0;
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$rules = [];
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$my_ticket = [];
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$nearby_tickets = [];
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foreach ($lines as $line) {
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if ($line === '') {
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$section += 1;
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} else {
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if ($line != 'your ticket:' && $line != 'nearby tickets:') {
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switch ($section) {
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case 0:
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$rules[] = parse_rule($line);
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break;
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case 1:
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$my_ticket = array_map(fn ($x) => (int)$x, explode(',', $line));
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break;
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case 2:
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$nearby_tickets[] = array_map(fn ($x) => (int)$x, explode(',', $line));
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break;
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}
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}
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}
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}
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return [$rules, $my_ticket, $nearby_tickets];
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}
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function parse_rule(string $line): array
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{
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[$name, $values] = array_map('trim', explode(':', $line));
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[$min_range, $max_range] = array_map('trim', explode(' or ', $values));
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[$min_min, $min_max] = array_map(fn ($x) => (int)$x, explode('-', $min_range));
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[$max_min, $max_max] = array_map(fn ($x) => (int)$x, explode('-', $max_range));
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return [$name, [$min_min, $min_max], [$max_min, $max_max]];
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}
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