PHP implements illegal word filtering (algorithm analysis)
Algorithm Introduction
Construct keywords into a tree, and each word is a node.
Traverse the statements that need to be filtered, and search each word of the statement in the tree to see if it exists.
Difficulties in implementation
Constructing a tree is simple. The key point is that traversing a string in php
requires you to correctly obtain the length of a single character.
The simple method of traversing a string is as follows:
$strLen = mb_strlen($str); for ($i = 0; $i < $strLen; $i++) { echo mb_substr($str, $i, 1, "utf8"),PHP_EOL; }
This method uses the mb_*
series of functions to correctly intercept each character. It is very slow when processing a large number of strings. I guess Yes: mb_substr
Every time a character is intercepted, the number of characters before the string must be calculated.
The correct way to traverse a string is to intercept the string according to the encoding rules of utf8
. Please see below for details.
Algorithm Implementation
<?php /** * 非法关键词检查 */ class SensitiveWords { protected $tree = null; protected $callIsNumeric = true; /** * 非法词汇列表,一个非法词汇占用一行 */ public function __construct($path = __DIR__ . '/sensitiveWords.txt') { $this->tree = new WordNode(); $file = fopen($path, "r"); while (!feof($file)) { $words = trim(fgets($file)); if ($words == '') { continue; } //存在纯数字的非法词汇 if (is_numeric($words)) { $this->callIsNumeric = false; } $this->setTree($words); } fclose($file); } protected function setTree($words) { $array = $this->strToArr($words); $tree = $this->tree; $l = count($array) - 1; foreach ($array as $k => $item) { $tree = $tree->getChildAlways($item); if ($l == $k) { $tree->end = true; } } } /** * 返回包含的非法词汇 * @param string $str * @return array */ public function check($str) { //先压缩字符串 $str = trim(str_replace([' ', "\n", "\r"], ['', '', ''], $str)); $ret = []; loop: $strLen = strlen($str); if ($strLen === 0) { return array_unique($ret); } //非法词汇中没有纯数字的非法词汇,待检测字符串又是纯数字的,则跳过不再检查 if ($this->callIsNumeric && is_numeric($str)) { return array_unique($ret); } //挨个字符进行判断 $tree = $this->tree; $words = ''; for ($i = 0; $i < $strLen; $i++) { //unicode范围 --> ord 范围 //一字节 0-127 --> 0 - 127 //二字节 128-2047 --> 194 - 223 //三字节 2048-65535 --> 224 - 239 //四字节 65536-1114111 --> 240 - 244 //@see http://shouce.jb51.net/gopl-zh/ch3/ch3-05.html $ord = ord($str[$i]); if ($ord <= 127) { $word = $str[$i]; } elseif ($ord <= 223) { $word = $str[$i] . $str[$i + 1]; $i += 1; } elseif ($ord <= 239) { $word = $str[$i] . $str[$i + 1] . $str[$i + 2]; $i += 2; } elseif ($ord <= 244) { //四字节 $word = $str[$i] . $str[$i + 1] . $str[$i + 2] . $str[$i + 3]; $i += 3; } else { //五字节php都溢出了 //Parse error: Invalid UTF-8 codepoint escape sequence: Codepoint too large continue; } //判断当前字符 $tree = $tree->getChild($word); if (is_null($tree)) { //当前字不存在,则截取后再次循环 $str = substr($str, $i + 1); goto loop; } else { $words .= $word; if ($tree->end) { $ret[] = $words; } } } return array_unique($ret); } protected function strToArr($str) { $array = []; $strLen = mb_strlen($str); for ($i = 0; $i < $strLen; $i++) { $array[] = mb_substr($str, $i, 1, "utf8"); } return $array; } } /** * 单个字符的节点 */ class WordNode { //是否为非法词汇末级节点 public $end = false; //子节点 protected $child = []; /** * @param string $word * @return WordNode */ public function getChildAlways($word) { if (!isset($this->child[$word])) { $this->child[$word] = new self(); } return $this->child[$word]; } /** * @param string $word * @return WordNode|null */ public function getChild($word) { if ($word === '') { return null; } if (isset($this->child[$word])) { return $this->child[$word]; } return null; } }
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