PHP 几种常用的算法整理

一、冒泡排序

<?php
$arr=array(1,5,9,7,2,8,4,3,6);
//控制冒泡的轮次
for($i=1;$i<count($arr);$i++) {
    //控制需要比较的次数，每轮冒出一个数
    for($k=0;$k<count($arr)-$i;$k++){
        if($arr[$k]>$arr[$k+1]){
            $tmp=$arr[$k+1];
            $arr[$k+1]=$arr[$k];
            $arr[$k]=$tmp;
        }
    }
}
print_r($arr);

二、利用PHP内置函数计算字符串长度

<?php
$str = "Hello,world";
$count =  0;
while (1){
    if (@$str[$count] != NULL){
        $count++;
        continue;
    }else{
        break;
    }
}
echo $count;

三、反向输出字符串

<?php
$str = "Hello,world";
if ($str == '') echo 0;
$bstr = "";
for ($i=(strlen($str)- 1); $i>=0; $i --){
    $bstr .= $str[$i ];
}
echo $bstr;

四、加密，解密

<?php
$str = "hello,world";
$key = "www.cnblogs.com";
$str = $str.$key;
$chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+";
$rand = rand(0,64);
$ch = $chars[$rand];
$mdKey = md5($key.$ch);
$mdKey = substr($mdKey,$rand%8, $rand%8+7);
$str = base64_encode($str);
$tmp = '';
$i=0;$j=0;$k = 0;
for ($i=0; $i<strlen($str); $i++) {
    $k = $k == strlen($mdKey) ? 0 : $k;
    $j = ($rand+strpos($chars,$str[$i])+ord($mdKey[$k++]))%64;
    $tmp .= $chars[$j];
}
echo urlencode(base64_encode($ch.$tmp));

<?php
$str = "YWFSU3FtUzYycDJJdlpSZDFuRGM1VjBFdVpRSm5udjN1bjAtTA%3D%3D";
$key = "www.cnblogs.com";
$str = base64_decode(urldecode($str));
$chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+";
$ch = $str[0];
$rand = strpos($chars,$ch);
$mdKey = md5($key.$ch);
$mdKey = substr($mdKey,$rand%8, $rand%8+7);
$str = substr($str,1);
$tmp = '';
$i=0;$j=0; $k = 0;
for ($i=0; $i<strlen($str); $i++) {
    $k = $k == strlen($mdKey) ? 0 : $k;
    $j = strpos($chars,$str[$i])-$rand - ord($mdKey[$k++]);
    while ($j<0) $j+=64;
    $tmp .= $chars[$j];
}
echo trim(base64_decode($tmp),$key);

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