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Fix monotone chain implementation

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This commit is contained in:
Dennis Eichhorn 2017-10-01 17:58:40 +02:00
parent dc5936565e
commit 043b0c70fe
1 changed files with 10 additions and 12 deletions
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22
Math/Geometry/ConvexHull/MonotoneChain.php
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@ -40,34 +40,32 @@ final class MonotoneChain
public static function createConvexHull(array $points) : array public static function createConvexHull(array $points) : array
{ {
if (($n = count($points)) > 1) { if (($n = count($points)) > 1) {
$k = 0;
$h = [];
uasort($points, [self::class, 'sort']); uasort($points, [self::class, 'sort']);
$k = 0;
$result = [];
// Lower hull // Lower hull
for ($i = 0; $i < $n; ++$i) { for ($i = 0; $i < $n; ++$i) {
while ($k >= 2 && self::cross($h[$k - 2], $h[$k - 1], $points[$i]) <= 0) { while ($k >= 2 && self::cross($result[$k - 2], $result[$k - 1], $points[$i]) <= 0) {
$k--; $k--;
} }
$h[$k++] = $points[$i]; $result[$k++] = $points[$i];
} }
// Upper hull // Upper hull
for ($i = $n - 2, $t = $k + 1; $i >= 0; $i--) { for ($i = $n - 2, $t = $k+1; $i >= 0; $i--) {
while ($k >= $t && self::cross($h[$k - 2], $h[$k - 1], $points[$i]) <= 0) { while ($k >= $t && self::cross($result[$k - 2], $result[$k - 1], $points[$i]) <= 0) {
$k--; $k--;
} }
$h[$k++] = $points[$i]; $result[$k++] = $points[$i];
} }
if ($k > 1) { ksort($result);
$h = array_splice($h, $k - 1);
}
return $h; return array_slice($result, 0, $k-1);
} }
return $points; return $points;