php实现的生成排列算法示例

本文实例讲述了php实现的生成排列算法。分享给大家供大家参考，具体如下：

<?php
function perm($s, $n, $index)
{
  if($n == 0)
  {
     return '';
  }
  else
  {
    $nIndex = count($index);  //可用的字符串下标
    $res = array();
    foreach($index as $i => $v)
    {
      $tmp = $index;
      unset($tmp[$i]);    //去掉当前的前缀
      /* 调试信息，便于理解
      echo "len $n , cur $i , index:\n";
      var_dump($tmp);
       */
      $ret = perm($s, $n-1, $tmp);  //递归得到稍短的排列
      if($ret != '')
      {
        foreach($ret as $r)
        {
          $res[] = $s[$v] . $r;  //将稍短的排列逐个拼上当前的前缀
        }
      }
      else
      {
        $res[] = $s[$v];
      }
    }
    return $res;
  }
}
function getPerm($s)
{
  $n = strlen($s);
  $index = range(0, $n-1);
  //得到不同长度的排列
  for($i=1; $i<=$n; $i++)
  {
    var_dump(perm($s, $i, $index));
  }
}
getPerm('abcd');
?>

运行结果：

array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
  [2]=>
  string(1) "c"
  [3]=>
  string(1) "d"
}
array(12) {
  [0]=>
  string(2) "ab"
  [1]=>
  string(2) "ac"
  [2]=>
  string(2) "ad"
  [3]=>
  string(2) "ba"
  [4]=>
  string(2) "bc"
  [5]=>
  string(2) "bd"
  [6]=>
  string(2) "ca"
  [7]=>
  string(2) "cb"
  [8]=>
  string(2) "cd"
  [9]=>
  string(2) "da"
  [10]=>
  string(2) "db"
  [11]=>
  string(2) "dc"
}
array(24) {
  [0]=>
  string(3) "abc"
  [1]=>
  string(3) "abd"
  [2]=>
  string(3) "acb"
  [3]=>
  string(3) "acd"
  [4]=>
  string(3) "adb"
  [5]=>
  string(3) "adc"
  [6]=>
  string(3) "bac"
  [7]=>
  string(3) "bad"
  [8]=>
  string(3) "bca"
  [9]=>
  string(3) "bcd"
  [10]=>
  string(3) "bda"
  [11]=>
  string(3) "bdc"
  [12]=>
  string(3) "cab"
  [13]=>
  string(3) "cad"
  [14]=>
  string(3) "cba"
  [15]=>
  string(3) "cbd"
  [16]=>
  string(3) "cda"
  [17]=>
  string(3) "cdb"
  [18]=>
  string(3) "dab"
  [19]=>
  string(3) "dac"
  [20]=>
  string(3) "dba"
  [21]=>