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advent_of_code_2021
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✨ Finit le jour 9

This commit is contained in:
Clement Desmidt 2021-12-10 16:10:34 +01:00
parent 592bc62c63
commit 23a90beb38
1 changed files with 99 additions and 0 deletions
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day_9/part_2.php Normal file
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<?php
$grid = array_map(static function ($row) {
return str_split($row);
}, explode("\n", file_get_contents('./input.txt')));
$points_in_bassin = [];
$low_points = [];
foreach ($grid as $i => $row) {
foreach ($row as $j => $cell) {
$count = 0;
if (!array_key_exists($i - 1, $grid) || $grid[$i - 1][$j] > $cell) {
$count++;
}
if (!array_key_exists($i + 1, $grid) || $grid[$i + 1][$j] > $cell) {
$count++;
}
if (!array_key_exists($j - 1, $row) || $row[$j - 1] > $cell) {
$count++;
}
if (!array_key_exists($j + 1, $row) || $row[$j + 1] > $cell) {
$count++;
}
if ($count === 4) {
$low_points[] = [$i, $j];
}
}
}
foreach ($low_points as $i => $low_point) {
$points_in_bassin[$i] = build_bassin($grid, [$low_point],0, [$low_point]);
}
rsort($points_in_bassin);
echo array_product(array_slice($points_in_bassin, 0, 3));
function build_bassin($grid, $neighbours, $count_neighbours = 0, $current_bassin = [])
{
$step = 0;
$new_neighbours = [];
foreach ($neighbours as $value) {
[$i, $j] = $value;
if (
isset($grid[$i][$j - 1]) &&
$grid[$i][$j - 1] != 9 &&
!in_array([$i, $j - 1], $current_bassin)
) {
$step++;
$count_neighbours++;
$current_bassin[] = [$i, $j - 1];
$new_neighbours[] = [$i, $j - 1];
}
if (
isset($grid[$i][$j + 1]) &&
$grid[$i][$j + 1] != 9 &&
!in_array([$i, $j + 1], $current_bassin)
) {
$step++;
$count_neighbours++;
$current_bassin[] = [$i, $j + 1];
$new_neighbours[] = [$i, $j + 1];
}
if (
isset($grid[$i - 1][$j]) &&
$grid[$i - 1][$j] != 9 &&
!in_array([$i - 1, $j], $current_bassin)
) {
$step++;
$count_neighbours++;
$current_bassin[] = [$i - 1, $j];
$new_neighbours[] = [$i - 1, $j];
}
if (
isset($grid[$i + 1][$j]) &&
$grid[$i + 1][$j] != 9 &&
!in_array([$i + 1, $j], $current_bassin)
) {
$step++;
$count_neighbours++;
$current_bassin[] = [$i + 1, $j];
$new_neighbours[] = [$i + 1, $j];
}
}
if ($step !== 0) {
return build_bassin($grid, $new_neighbours, $count_neighbours, $current_bassin, 1);
}
return $count_neighbours + 1;
}