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<?php
declare(strict_types=1);
namespace leetcode;
class CountingBits
{
public static function countBits(int $num): array
if ($num <= 0) {
return [];
}
$bits = array_fill(0, $num + 1, 0);
for ($i = 1; $i <= $num; $i++) {
$bits[$i] = $bits[$i & ($i - 1)] + 1;
return $bits;
public static function countBits2(int $num): array
$bits[0] = 0;
$bits[$i] = ($i & 1) === 0 ? $bits[$i >> 1] : $bits[$i - 1] + 1;
public static function countBits3(int $num): array
$pow = 1;
for ($i = 1, $t = 0; $i <= $num; $i++, $t++) {
if ($i === $pow) {
$pow *= 2;
$t = 0;
$bits[$i] = $bits[$t] + 1;
public static function countBits4(int $num): array
$bits[$i] = $bits[$i / 2] + $i % 2;