100 lines
2.5 KiB
PHP
100 lines
2.5 KiB
PHP
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<?php
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$grid = array_map(static function ($row) {
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return str_split($row);
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}, explode("\n", file_get_contents('./input.txt')));
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$points_in_bassin = [];
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$low_points = [];
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foreach ($grid as $i => $row) {
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foreach ($row as $j => $cell) {
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$count = 0;
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if (!array_key_exists($i - 1, $grid) || $grid[$i - 1][$j] > $cell) {
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$count++;
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}
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if (!array_key_exists($i + 1, $grid) || $grid[$i + 1][$j] > $cell) {
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$count++;
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}
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if (!array_key_exists($j - 1, $row) || $row[$j - 1] > $cell) {
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$count++;
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}
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if (!array_key_exists($j + 1, $row) || $row[$j + 1] > $cell) {
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$count++;
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}
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if ($count === 4) {
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$low_points[] = [$i, $j];
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}
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}
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}
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foreach ($low_points as $i => $low_point) {
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$points_in_bassin[$i] = build_bassin($grid, [$low_point],0, [$low_point]);
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}
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rsort($points_in_bassin);
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echo array_product(array_slice($points_in_bassin, 0, 3));
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function build_bassin($grid, $neighbours, $count_neighbours = 0, $current_bassin = [])
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{
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$step = 0;
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$new_neighbours = [];
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foreach ($neighbours as $value) {
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[$i, $j] = $value;
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if (
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isset($grid[$i][$j - 1]) &&
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$grid[$i][$j - 1] != 9 &&
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!in_array([$i, $j - 1], $current_bassin)
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) {
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$step++;
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$count_neighbours++;
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$current_bassin[] = [$i, $j - 1];
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$new_neighbours[] = [$i, $j - 1];
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}
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if (
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isset($grid[$i][$j + 1]) &&
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$grid[$i][$j + 1] != 9 &&
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!in_array([$i, $j + 1], $current_bassin)
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) {
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$step++;
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$count_neighbours++;
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$current_bassin[] = [$i, $j + 1];
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$new_neighbours[] = [$i, $j + 1];
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}
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if (
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isset($grid[$i - 1][$j]) &&
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$grid[$i - 1][$j] != 9 &&
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!in_array([$i - 1, $j], $current_bassin)
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) {
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$step++;
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$count_neighbours++;
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$current_bassin[] = [$i - 1, $j];
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$new_neighbours[] = [$i - 1, $j];
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}
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if (
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isset($grid[$i + 1][$j]) &&
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$grid[$i + 1][$j] != 9 &&
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!in_array([$i + 1, $j], $current_bassin)
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) {
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$step++;
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$count_neighbours++;
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$current_bassin[] = [$i + 1, $j];
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$new_neighbours[] = [$i + 1, $j];
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}
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}
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if ($step !== 0) {
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return build_bassin($grid, $new_neighbours, $count_neighbours, $current_bassin, 1);
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}
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return $count_neighbours + 1;
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}
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