142 lines
3.2 KiB
PHP
142 lines
3.2 KiB
PHP
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<?php
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$input_file = '../inputs/day12.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$instructions = array_map('trim', explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($instructions) . "\n";
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print 'Part 2 answer: ' . solve_part_two($instructions) . "\n";
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}
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}
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function solve_part_one(array $instructions): int
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{
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$state = new day12_state();
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foreach (parse_instructions($instructions) as $instruction) {
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$state = move($instruction, $state);
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}
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return abs($state->v_pos) + abs($state->h_pos);
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}
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function solve_part_two(array $instructions): int
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{
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$state = new day12_state();
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foreach (parse_instructions($instructions) as $instruction)
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$state = move_with_waypoint($instruction, $state);
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return abs($state->v_pos) + abs($state->h_pos);
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}
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function move(array $instruction, day12_state $state): day12_state
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{
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switch ($instruction[0]) {
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case 'N':
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$state->v_pos += $instruction[1];
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break;
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case 'S':
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$state->v_pos -= +$instruction[1];
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break;
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case 'E':
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$state->h_pos += $instruction[1];
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break;
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case 'W':
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$state->h_pos -= $instruction[1];
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break;
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case 'F':
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switch ($state->facing_direction % 4) {
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case 0:
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$state->v_pos += $instruction[1];
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break;
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case 1:
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$state->h_pos += $instruction[1];
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break;
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case 2:
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$state->v_pos -= $instruction[1];
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break;
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case 3:
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$state->h_pos -= $instruction[1];
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break;
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}
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break;
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case 'R':
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$state->facing_direction += ($instruction[1] / 90);
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break;
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case 'L':
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$state->facing_direction -= ($instruction[1] / 90);
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break;
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}
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if ($state->facing_direction < 0)
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$state->facing_direction += 4; // NOT THAT EASY, need to wrap around 0
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return $state;
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}
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function move_with_waypoint(array $instruction, day12_state $state): day12_state
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{
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switch ($instruction[0]) {
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case 'N':
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$state->w_v_pos += $instruction[1];
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break;
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case 'S':
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$state->w_v_pos -= +$instruction[1];
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break;
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case 'E':
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$state->w_h_pos += $instruction[1];
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break;
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case 'W':
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$state->w_h_pos -= $instruction[1];
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break;
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case 'F':
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for ($i = 0; $i < $instruction[1]; $i++) {
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$state->v_pos += $state->w_v_pos;
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$state->h_pos += $state->w_h_pos;
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}
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break;
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case 'R':
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for ($i = 0; $i < $instruction[1] / 90; $i++) {
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$new_v_pos = -$state->w_h_pos;
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$new_h_pos = $state->w_v_pos;
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$state->w_v_pos = $new_v_pos;
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$state->w_h_pos = $new_h_pos;
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}
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break;
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case 'L':
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for ($i = 0; $i < $instruction[1] / 90; $i++) {
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$new_v_pos = $state->w_h_pos;
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$new_h_pos = -$state->w_v_pos;
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$state->w_v_pos = $new_v_pos;
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$state->w_h_pos = $new_h_pos;
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}
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break;
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}
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return $state;
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}
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function parse_instructions(array $instructions): array
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{
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$parsed_instructions = [];
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foreach ($instructions as $instruction) {
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if (preg_match('/^([NSEWLRF])(\d+)$/', trim($instruction), $matches)) {
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[, $inst, $arg] = $matches;
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$parsed_instructions[] = [$inst, $arg];
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}
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}
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return $parsed_instructions;
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}
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class day12_state
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{
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public int $v_pos = 0;
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public int $h_pos = 0;
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public int $w_v_pos = 1;
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public int $w_h_pos = 10;
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public int $facing_direction = 1; // N = 0, E = 1, S = 2, W = 3
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}
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