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Reversing a String in PHP

Reversing a string is a common algorithm task. Depending on your level of expertise, you might choose different approaches.

1. Junior Level: Built-in Function​

The simplest and most efficient way for basic ASCII strings is using the built-in strrev() function.

function reverseString(string $str): string
{
    return strrev($str);
}

echo reverseString("hello"); // "olleh"

2. Middle Level: Manual Loop​

A manual implementation shows you understand that a string can be treated as an array of bytes. However, this method is not multi-byte safe (it will break characters like emoji or Cyrillic).

function reverseStringLoop(string $str): string
{
    $reversed = '';
    $length = strlen($str);
    for ($i = $length - 1; $i >= 0; $i--) {
        $reversed .= $str[$i];
    }
    return $reversed;
}

3. Senior Level: Multi-byte (UTF-8) Safe​

Modern applications often use UTF-8. Built-in strrev() and manual byte-loops will corrupt multi-byte characters. A Senior developer should be aware of this and provide a solution using multi-byte aware functions like mb_str_split().

Using mb_str_split()​

This method is efficient and flexible for handling UTF-8 characters correctly.

/**
 * Reverse a multi-byte string.
 */
function mb_strrev(string $string, string $encoding = null): string
{
    $chars = mb_str_split($string, 1, $encoding ?: mb_internal_encoding());
    return implode('', array_reverse($chars));
}

echo mb_strrev("Привет"); // "тевирП"
echo mb_strrev("👋🌍");   // "🌍👋"

Using recursion (Alternative)​

While not the most efficient for large strings, it demonstrates algorithmic thinking.

function reverseRecursive(string $str): string
{
    if (mb_strlen($str) <= 1) {
        return $str;
    }
    return reverseRecursive(mb_substr($str, 1)) . mb_substr($str, 0, 1);
}