Example of string matching algorithm implemented in PHP
This article mainly introduces the string matching algorithm implemented by PHP, briefly describes the concept and principle of the sunday algorithm, and analyzes the related skills of PHP based on the sunday algorithm to implement string matching operations in the form of examples. Friends in need can refer to Next
The example in this article describes the string matching algorithm implemented by PHP——Sunday algorithm. Share it with everyone for your reference, the details are as follows:
The Sunday algorithm is a string pattern matching proposed by Daniel M. Sunday in 1990. The core idea is: During the matching process, when the pattern string is found to be unmatched, the algorithm can skip as many characters as possible for the next step of matching, thus improving the matching efficiency.
<?php
/*
*@param $pattern 模式串
*@param $text 待匹配串
*/
function mySunday($pattern = '',$text = ''){
if(!$pattern || !$text) return false;
$pattern_len = mb_strlen($pattern);
$text_len = mb_strlen($text);
if($pattern_len >= $text_len) return false;
$i = 0;
for($i = 0; $i < $pattern_len; $i++){ //组装以pattern中的字符为下标的数组
$shift[$pattern[$i]] = $pattern_len - $i;
}
while($i <= $text_len - $pattern_len){
$nums = 0; //匹配上的字符个数
while($pattern[$nums] == $text[$i + $nums]){
$nums++;
if($nums == $pattern_len){
return "The first match index is $i\n";
}
}
if($i + $pattern_len < $text_len && isset($shift[$text[$i + $pattern_len]])){ //判断模式串后一位字符是否在模式串中
$i += $shift[$text[$i + $pattern_len]]; //对齐该字符
}else{
$i += $pattern_len; //直接滑动pattern_len位
}
}
}
$text = "I am testing mySunday on sunday!";
$pattern = "sunday";
echo mySunday($pattern,$text);Run result:
The first match index is 25
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