如何在php中输出所有可能的字符串（39个非十亿字符串）混合符号输出一个站点地图

Question

我有用户帐户规则是限制20个符号可以是字母，句点，下划线和数字。
q1。如何打印所有可能的字符串？下面是我的代码我找不到混合不同符号的方式
q2。这是正确的方式打印网站的网站地图，因为它是39非货币字符串，我发现https://stackoverflow.com/a/1099421，但我需要知道更多的细节了解通常人们如何做到这一点？

$letters = array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'); 
$period = array('.'); 
$underscore = array('_'); 
$numbers = array('0','1','2','3','4','5','6','7','8','9'); 

for ($i=0; $i < count($letters); $i++) { 
    for ($ii=0; $ii < count($period); $ii++) { 
    for ($iii=0; $iii < count($underscore); $iii++) { 
     for ($iiii=0; $iiii < count($numbers); $iiii++) { 
     // echo $numbers[$iiii]+$letters[$i]+ ... 
     } 
    } 
    } 
} 

编辑：
下面的回答我尝试做一个XML站点地图中，但它循环只有一个符号长度的基础？

$domDocument = new DOMDocument('1.0', 'UTF-8'); 

$domElementUrlSet = $domDocument->createElement('urlset'); 
$domElementUrlSet->appendChild(
    new DomAttr('xmlns', 'http://www.sitemaps.org/schemas/sitemap/0.9') 
); 

$domDocument->appendChild($domElementUrlSet); 



$chars = array(
    'a','b','c','d','e','f','g','h', 
    'i','j','k','l','m','n','o','p', 
    'q','r','s','t','u','v','w','x', 
    'y','z','.','_','0','1','2','3', 
    '4','5','6','7','8','9' 
); 
$length = 2; 
$charsLength = count($chars); 
$current = array_fill(0, $length, -1); 
$end = array_fill(0, $length, $charsLength - 1); 

while ($current != $end) { 
    // increment current state 
    $n = $length; 
    while ($n-- >= 0) { 
     $current[$n]++; 
     if ($current[$n] == $charsLength) { 
      $current[$n] = 0; 
     } else { 
      break; 
     } 
    } 
    // print string 
    for ($i=0; $i < $length; $i++) { 
     if ($current[$i] >= 0) { 
     // echo $chars[$current[$i]]; 

     $url = $domDocument->createElement('url'); 
     $url->appendChild($loc = $domDocument->createElement('loc', 'http://www.example.com/'.$chars[$current[$i]])); 

     $domElementUrlSet->appendChild($url); 
     } 
    } 
    // echo PHP_EOL; 
} 

echo $domDocument->saveXML(); 

Answer 1

任务非常微不足道。你不需要单独的字符集，只需要单个字母并遍历所有可能的组合：

<?php 
$chars = array(
    'a','b','c','d','e','f','g','h', 
    'i','j','k','l','m','n','o','p', 
    'q','r','s','t','u','v','w','x', 
    'y','z','.','_','0','1','2','3', 
    '4','5','6','7','8','9' 
); 
$length = 20; 
$charsLength = count($chars); 
$current = array_fill(0, $length, -1); 
$end = array_fill(0, $length, $charsLength - 1); 

while ($current != $end) { 
    // increment current state 
    $n = $length; 
    while ($n-- >= 0) { 
     $current[$n]++; 
     if ($current[$n] == $charsLength) { 
      $current[$n] = 0; 
     } else { 
      break; 
     } 
    } 
    // print string 
    for ($i=0; $i < $length; $i++) { 
     if ($current[$i] >= 0) echo $chars[$current[$i]]; 
    } 
    echo PHP_EOL; 
}