<?php

class LCS
{
    public $str1;
    public $str2;
    public $c = array();
    /*返回串一和串二的最长公共子序列
     */
    public function getLCS($str1, $str2, $len1 = 0, $len2 = 0)
    {
        $this->str1 = $str1;
        $this->str2 = $str2;
        if ($len1 == 0)
        {
            $len1 = strlen($str1);
        }

        if ($len2 == 0)
        {
            $len2 = strlen($str2);
        }

        $this->initC($len1, $len2);
        return $this->printLCS($this->c, $len1 - 1, $len2 - 1);
    }
    /*返回两个串的相似度
     */
    public function getSimilar($str1, $str2)
    {
        $len1 = strlen($str1);
        $len2 = strlen($str2);
        $len  = strlen($this->getLCS($str1, $str2, $len1, $len2));
        return $len * 2 / ($len1 + $len2);
    }
    public function initC($len1, $len2)
    {
        for ($i = 0; $i < $len1; $i++)
        {
            $this->c[$i][0] = 0;
        }

        for ($j = 0; $j < $len2; $j++)
        {
            $this->c[0][$j] = 0;
        }

        for ($i = 1; $i < $len1; $i++)
        {
            for ($j = 1; $j < $len2; $j++)
            {
                if ($this->str1[$i] == $this->str2[$j])
                {
                    $this->c[$i][$j] = $this->c[$i - 1][$j - 1] + 1;
                }
                else if ($this->c[$i - 1][$j] >= $this->c[$i][$j - 1])
                {
                    $this->c[$i][$j] = $this->c[$i - 1][$j];
                }
                else
                {
                    $this->c[$i][$j] = $this->c[$i][$j - 1];
                }
            }
        }
    }
    public function printLCS($c, $i, $j)
    {
        if ($i == 0 || $j == 0)
        {
            if ($this->str1[$i] == $this->str2[$j])
            {
                return $this->str2[$j];
            }
            else
            {
                return "";
            }

        }
        if ($this->str1[$i] == $this->str2[$j])
        {
            return $this->printLCS($this->c, $i - 1, $j - 1) . $this->str2[$j];
        }
        else if ($this->c[$i - 1][$j] >= $this->c[$i][$j - 1])
        {
            return $this->printLCS($this->c, $i - 1, $j);
        }
        else
        {
            return $this->printLCS($this->c, $i, $j - 1);
        }
    }
}

$lcs = new LCS();

echo $lcs->getSimilar("hello wang", "hello feng");