Minimum window substring

minsubstring.php

<?php

$str = 'abbaacdbcab';
$chars = ['a', 'b', 'c'];

echo "Expected: bca | Result: ".findMinWinSubString($str, $chars)."\n";

$str = 'xyyzyzyx';
$chars = ['x', 'y', 'z'];

echo "Expected: xyz | Result: ".findMinWinSubString($str, $chars)."\n";

function findMinWinSubString($str, $chars) {
    $right = 0;
    $left = 0;
    
    $checkWindow = [];
    $uniqueCounter = 0;
    $requiredCounter = count($chars);
    
    foreach($chars as $char) {
        
        if (!isset($checkWindow[$char])) {
            $checkWindow[$char] = 0;
        }
        
        $checkWindow[$char] += 1; 
    }
    
    $minWindow = [];
    while ($right < strlen($str)) {
        
        $char = $str[$right];
        
        if (!isset($minWindow[$char])) {
            $minWindow[$char] = 0;
        }
        
        
        if (in_array($char, $chars) && $minWindow[$char] == 0) {
            $uniqueCounter += 1;
        }
        
        
        $minWindow[$char] += 1;
        
        while ($uniqueCounter == $requiredCounter) {
        
            $length = $right - $left + 1;
            
        
            if ($length === $uniqueCounter && $uniqueCounter == $requiredCounter) {
                return substr($str, $left, $length);
            }
            
            $headChar = $str[$left];
            
            $minWindow[$headChar] -= 1;
            
            if ($minWindow[$headChar] == 0 && in_array($headChar, $chars)) {
                $uniqueCounter -= 1;
            }
            
            $left += 1;
        }
        
        $right += 1;
    }
}