BBS水木清华站∶精华区

发信人: thinkin (强强), 信区: Linux
标  题: "In String" function
发信站: BBS 水木清华站 (Thu Feb 17 10:58:35 2000)

<?php
/* This function returns the position of string s1 within string s2.
   The position is 1 based.  If s1 is not in s2, 0 is returned.
*/
function InStr($s1, $s2)
{
     //Check for valid input
    if(!(is_string($s1) && is_string($s2))) return 0;
    $s1len = strlen($s1);
    $s2len = strlen($s2);
     //Check if s1 in s2 at all
    if(!ereg($s1, $s2)) return 0;
     //Resolve simple case
    if($s1 == $s2) return 1;
     //Set initial search limits
    $begin = 0;
    $end = $s2len - $s1len;
     //Initialize position
    $position = 0;
     //Do binary search of s2 for s1
     //Check left side first to find first occurance of s1
     //Check right side first to find last occurance of s1
    while($end > $begin + 1)
    {
        $middle = ceil(($begin + $end) / 2);
        $leftBegin = $begin;
        $rightBegin = $middle + $s1len;
        $leftEnd = $middle;
        $rightEnd = $end + $s1len;
         //Check left first
        if(ereg($s1, substr($s2, $leftBegin, $rightBegin - $leftBegin)))
        {
            $end = $middle;
        }
        else  //(ereg($s1, substr($s2, $leftEnd, $rightEnd - $leftEnd)))
        {
            $position += $middle - $begin;
            $begin = $middle;
        }
    }
     //Resolve 1 off problems introduced by ceil
    if(ereg($s1, substr($s2, $end, $s1len))) $position++;
     //Return position 1 based
    return $position + 1;
}
?>
--

人生到处知何似？
    应似飞鸿踏雪泥。
        泥上偶然留指爪，
            鸿飞那复计东西！


※ 来源:·BBS 水木清华站 smth.org·[FROM: 162.105.37.191]