<?php

/*
 * This file is part of the Jiannei/lumen-api-starter.
 *
 * (c) Jiannei <longjian.huang@foxmail.com>
 *
 * This source file is subject to the MIT license that is bundled
 * with this source code in the file LICENSE.
 */

namespace App\Services;


class CombinationService
{
    public static function combination($arr, $num)
    {
        $r = array();

        $n = count($arr);
        if ($num <= 0 || $num > $n) {
            return $r;
        }

        for ($i = 0; $i < $n; $i++) {
            $t = array($arr[$i]);
            if ($num == 1) {
                $r[] = $t;
            } else {
                $b = array_slice($arr, $i + 1);
                $c = self::combination($b, $num - 1);
                foreach ($c as $v) {
                    $r[] = array_merge($t, $v);
                }
            }
        }

        return $r;
    }

    public static function combinationALL($array, $level = -1, &$list = [])
    {
        for ($i = 0; $i < count($array); $i++) {
            if ($level < 0) {
                //第一级直接输出对应数字
                $list[][] = $array[$i];
            } else {
                $values = $array[$i];
                //根据等级组装前几位
                for ($k = 0; $k < $level; $k++) {
                    $values .= '+' . $array[$i + $k + 1];
                }
                $j = 0;
                //循环拼合最后一位
                for ($n = ($i + $level + 1); $n < count($array); $n++) {
                    $j++;
                    $first = $values; // 组合上几位
                    $first .= '+' . $array[$n];
                    $list[] = str2arr($first, '+');
                }

                //到最后一位结束递归
                if ($j == 1) {
                    break;
                }
            }

        }
        //长度大于等级+2停止递归
        if (($level + 2) < count($array)) {
            self::combinationALL($array, $level + 1, $list);
        }
        return $list;
    }

}