某些业务场景下，我们会用到组合穷举方法，这里整理几个穷举方法

1、不限顺序的数组组合穷举：

  1. <?php
  2. //索引位置
  3. function getAnswer($amount, $need){
  4.     if($need == 1){
  5.         for ($i=1;$i<=$amount;$i++){
  6.             $rst[] = [$i];
  7.         }
  8.         return $rst;
  9.     }else{
  10.         $rst = getAnswer($amount-1, $need-1);
  11.         foreach($rst as $v){
  12.             for ($i=$v[$need-2]+1;$i<=$amount;$i++){
  13.                 $v[$need-1] = $i;
  14.                 $result[] = $v;
  15.             }
  16.         }
  17.         return $result;
  18.     }
  19. }
  20. //通过索引取数组值
  21. function getFinallyAnswer($array, $pick){
  22.     $amount = count($array);
  23.     $sub = getAnswer($amount, $pick);
  24.     foreach ($sub as $k => $v){
  25.         foreach ($v as $per_sub){
  26.             $rst[$k][] = $array[$per_sub - 1];
  27.         }
  28.     }
  29.     return $rst;
  30. }
  32. //穷举算法
  33. function getSequenceAry($arr)
  34. {
  35.     if (count($arr) == 1) {
  36.         return array($arr);
  37.     }
  38.     $arrRet = array();
  39.     foreach ($arr as $k => $v) {
  40.         $arr2 = $arr;
  41.         unset($arr2[$k]);
  42.         $arrOrderList = getSequenceAry($arr2);
  43.         foreach ($arrOrderList as $order) {
  44.             array_unshift($order, $v);
  45.             $arrRet[] = $order;
  46.         }
  47.     }
  48.     return $arrRet;
  49. }
  50. echo count(getFinallyAnswer(array(1,2,3,4,5,6,7,8),5));
  51. //print_r(getSequenceAry(array(1,2,3,4)));
  52. print_r(getAnswer(8,5));