php – 具有错误字符容差的最长Common Substring

此代码基于http://en.wikipedia.org/wiki/Wagner%E2%80%93Fischer_algorithm和http://en.wikipedia.org/wiki/Approximate_string_matching#Problem_formulation_and_algorithms

给出$needle,它返回$haystack的一个(可能是几个)最小levenshtein子串.现在,levenshtein距离只是编辑距离的一个衡量标准,它可能实际上并不适合您的需求. ‘hte’在这个指标上更接近’他’而不是”’.我提出的一些例子表明了这种技术的局限性.我相信这比我之前给出的答案要可靠得多,但让我知道它对你有什么用.

// utility function - returns the key of the array minimum
function array_min_key($arr)
{
    $min_key = null;
    $min = PHP_INT_MAX;
    foreach($arr as $k => $v) {
        if ($v < $min) {
            $min = $v;
            $min_key = $k;
        }
    }
    return $min_key;
}

// Calculate the edit distance between two strings
function edit_distance($string1,$string2)
{
    $m = strlen($string1);
    $n = strlen($string2);
    $d = array();

    // the distance from '' to substr(string,$i)
    for($i=0;$i<=$m;$i++) $d[$i][0] = $i;
    for($i=0;$i<=$n;$i++) $d[0][$i] = $i;

    // fill-in the edit distance matrix
    for($j=1; $j<=$n; $j++)
    {
        for($i=1; $i<=$m; $i++)
        {
            // Using,for example,the levenshtein distance as edit distance
            list($p_i,$p_j,$cost) = levenshtein_weighting($i,$j,$d,$string1,$string2);
            $d[$i][$j] = $d[$p_i][$p_j]+$cost;
        }
    }

    return $d[$m][$n];
}

// Helper function for edit_distance()
function levenshtein_weighting($i,$string2)
{
    // if the two letters are equal,cost is 0
    if($string1[$i-1] === $string2[$j-1]) {
        return array($i-1,$j-1,0);
    }

    // cost we assign each operation
    $cost['delete'] = 1;
    $cost['insert'] = 1;
    $cost['substitute'] = 1;

    // cost of operation + cost to get to the substring we perform it on
    $total_cost['delete'] = $d[$i-1][$j] + $cost['delete'];
    $total_cost['insert'] = $d[$i][$j-1] + $cost['insert'];
    $total_cost['substitute'] = $d[$i-1][$j-1] + $cost['substitute'];

    // return the parent array keys of $d and the operation's cost
    $min_key = array_min_key($total_cost);
    if ($min_key == 'delete') {
        return array($i-1,$cost['delete']);
    } elseif($min_key == 'insert') {
        return array($i,$cost['insert']);
    } else {
        return array($i-1,$cost['substitute']);
    }
}

// attempt to find the substring of $haystack most closely matching $needle
function shortest_edit_substring($needle,$haystack)
{
    // initialize edit distance matrix
    $m = strlen($needle);
    $n = strlen($haystack);
    $d = array();
    for($i=0;$i<=$m;$i++) {
        $d[$i][0] = $i;
        $backtrace[$i][0] = null;
    }
    // instead of strlen,we initialize the top row to all 0's
    for($i=0;$i<=$n;$i++) {
        $d[0][$i] = 0;
        $backtrace[0][$i] = null;
    }

    // same as the edit_distance calculation,but keep track of how we got there
    for($j=1; $j<=$n; $j++)
    {
        for($i=1; $i<=$m; $i++)
        {
            list($p_i,$needle,$haystack);
            $d[$i][$j] = $d[$p_i][$p_j]+$cost;
            $backtrace[$i][$j] = array($p_i,$p_j);
        }
    }

    // now find the minimum at the bottom row
    $min_key = array_min_key($d[$m]);
    $current = array($m,$min_key);
    $parent = $backtrace[$m][$min_key];

    // trace up path to the top row
    while(! is_null($parent)) {
        $current = $parent;
        $parent = $backtrace[$current[0]][$current[1]];
    }

    // and take a substring based on those results
    $start = $current[1];
    $end = $min_key;
    return substr($haystack,$start,$end-$start);
}

// some testing
$data = array( array('foo',' foo'),array('fat','far'),array('dat burn','rugburn'));
$data[] = array('big yellow school bus','they rode the bigyellow schook bus that afternoon');
$data[] = array('bus','they rode the bigyellow schook bus that afternoon');
$data[] = array('big','they rode the bigyellow schook bus that afternoon');
$data[] = array('nook','they rode the bigyellow schook bus that afternoon');
$data[] = array('they','console,controller and games are all in very good condition,only played occasionally. includes power cable,controller charge cable and audio cable. smoke free house. pes 2011 super street fighter');
$data[] = array('controker',controller charge cable and audio cable. smoke free house. pes 2011 super street fighter');

foreach($data as $dat) {
    $substring = shortest_edit_substring($dat[0],$dat[1]);
    $dist = edit_distance($dat[0],$substring);
    printf("Found |%s| in |%s|,matching |%s| with edit distance %dn",$substring,$dat[1],$dat[0],$dist);
}