PHP - Check if a string is a rotation of another string

Question

Need to write a code block which check is one string is a rotation of another.

Looked at loads of posts on here and it is all in Java or C++ but I need to do it in PHP.

I have tried a few different things, trying to work from the C++ and Java examples but I am not having any luck, here is my current code:

<?php

function isSubstring($s1, $s2) {


    if(strlen($s1) != strlen($s2)) {
        return false;
    }

    if(WHAT TO PUT HERE) {
        echo "it is!";
    } else {
        echo "nope";
    }
}


isSubstring("hello", "helol");

?>

Answer 1

Many ways available. Here one more using built-in function count_chars on both strings, and then comparing both resulting arrays :

function isSubstring($s1, $s2) {
    if (strlen($s1) != strlen($s2)) {
        echo "nope";
        return;
    }

    $s1cnt = count_chars($s1, 1);
    $s2cnt = count_chars($s2, 1);

    if($s1cnt === $s2cnt) {
        echo "it is!";
    } else {
        echo "nope";
    }
}

Edit : as MonkeyZeus pointed out, beware of comparison with multibyte characters. It may bite a little bit :

isSubstring('crढap', 'paࢤrc');

will give true as answer. ढ is UTF-8 indian devanagari three byte char : E0 A2 A4 and ࢤ is also three byte chars (arabic) : E0 A4 A2, and the count_chars function counts the individual bytes. So it would be safe to use if chars are from only one language, else get some headache pills...

It seems to me that to manage this kind of things we need to have chars that are made of 3 bytes.

Answer 2

I would go for something like this:

function isSubstring($s1, $s2)
{
    // If the strings match exactly then no need to proceed
    if($s1 === $s2)
    {
        echo "it is!";
        return;
    }
    elseif(strlen($s1) !== strlen($s2))
    {
        // Strings must be of equal length or else no need to proceed
        echo "nope";
        return;
    }

    // Put each character into an array
    $s1 = str_split($s1);
    $s2 = str_split($s2);

    // Sort alphabetically based on value
    sort($s1);
    sort($s2);

    // Triple check the arrays against one-another
    if($s1 === $s2)
    {
        echo "it is!";
    }
    else
    {
        echo "nope";
    }
}

Answer 3

Here is a multibyte safe function to compare the two strings:

function mb_isAnagram($s1, $s2) {
    if (strlen($s1) != strlen($s2)) {
        return false;
    } else {
        $c1 = preg_split('//u', $s1, null, PREG_SPLIT_NO_EMPTY);
        $c2 = preg_split('//u', $s2, null, PREG_SPLIT_NO_EMPTY);
        sort($c1);
        sort($c2);
        if ($c1 === $c2) {
            return true;
        } else {
            return false;
        }
    }
}

Answer 4

You could split each string and sort it, like this:

$split1 = unpack("C*",$s1);
asort($split1);

Then you can traverse both arrays comparing the values.

Answer 5

<?php
function isRotationalString($str1,$str2){
    $len = strlen($str1); 
    if($str1 === $str2){
        return true;
    }else{
        if($len == strlen($str2)){
            $flag = true;
            for($i=0;$i<$len;$i++){
                if($str1[0]==$str2[$i]){
                    $tst = $i;$start = true;break;
                }
            }
            if($start){
                for($j=0;$j<$len;$j++){
                    $m = $j+$tst; 
                    if($m < $len){
                        if($str1[$j] != $str2[$m]){
                            $flag = false;break;
                        }
                    }else{
                        if($m>=$len)
                        {
                            $k = $m - $len;
                            if($str1[$j] != $str2[$k]){
                                $flag = false;break;   
                            }
                        }
                    }      
                }  
            }else{
                $flag = false;
            }
            return $flag;
        }
    }
}
echo isRotationalString("abcd","bcda")?'It is':'It is not';
?>

above script will check whether a string is a rotation of another string or not?
isRotationalString("abcd","bcda") => It is
isRotationalString("abcd","cbda") => It is Not

Answer 6

This is the function for string rotation.

echo isRotationalString("abcdef","efabcd")?'It is':'It is not';

function isRotationalString($str1,$str2){
    $len = strlen($str1); 
    if($str1 === $str2){
        return true;
    } else {
        if($len == strlen($str2)) {
    
            $stringMatchedArr1 = $stringMatchedArr2 = [];
            for($i=0; $i<$len; $i++) {
                $substr = substr($str1,$i );
                $pos = strpos($str2, $substr);
                if($pos !== false) {
                    $stringMatchedArr1[] = $substr;
                }
            }
        
            for($j=1; $j <= $len; $j++) {
                $substr = substr($str1, 0, $j );
                $pos = strpos($str2, $substr);
                if($pos !== false) {
                    $stringMatchedArr2[] = $substr;
                }
            }
        
            foreach($stringMatchedArr2 as  $string1) {
                foreach($stringMatchedArr1 as $string2) {
                    if($string1.$string2 == $str1)
                         return true;
                }
            }
       
        }
    }
}

Answer 7

I would sort the characters in the strings by making it an array and then imploding them to a string again.

if (sort(str_split($s1)) == sort(str_split($s2))) {

That would do the trick in one line.

Edit: Thanks Don't Panic, edited my answer!