Utils.php
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Utils.php
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	<?php

	namespace Tests;

	/**
	* Small utility functions for tests
	*/
	class Utils
	{
	/**
	* Provide all unique combinations of elements in $input, with order and duplicates irrelevant.
	*
	* @param array $input the input array of elements
	*
	* @return array[]
	*/
	public static function powerSet(array $input): array
	{
	$output = [];

	for ($x = 0; $x < count($input); $x++) {
	self::combine($input, $x + 1, 0, [], 0, $output);
	}

	return $output;
	}

	private static function combine($input, $r, $index, $data, $i, &$output): void
	{
	$n = count($input);

	// Current cobination is ready
	if ($index == $r) {
	$output[] = array_slice($data, 0, $r);
	return;
	}

	// When no more elements are there to put in data[]
	if ($i >= $n) {
	return;
	}

	// current is included, put next at next location
	$data[$index] = $input[$i];
	self::combine($input, $r, $index + 1, $data, $i + 1, $output);

	// current is excluded, replace it with next (Note that i+1
	// is passed, but index is not changed)
	self::combine($input, $r, $index, $data, $i + 1, $output);
	}
	}