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<?php
declare(strict_types=1);
namespace leetcode;
use leetcode\util\TreeNode;
class UniqueBinarySearchTreesII
{
public static function generateTrees(int $n): array
if ($n <= 0) {
return [];
}
return self::helper(1, $n);
private static function helper(int $start, int $end): array
$ans = [];
if ($start > $end) {
$ans[] = null;
for ($i = $start; $i <= $end; $i++) {
$lefts = self::helper($start, $i - 1);
$rights = self::helper($i + 1, $end);
foreach ($lefts as $left) {
foreach ($rights as $right) {
$root = new TreeNode($i);
$root->left = $left;
$root->right = $right;
$ans[] = $root;
return $ans;
imajinyun /
leetcode-php
