Original problem

https://leetcode.com/problems/make-the-string-great/

Original text

Description

Given a string s of lower and upper case English letters.

A good string is a string which doesn’t have two adjacent characters s[i] and s[i + 1] where:

  • 0 <= i <= s.length - 2
  • s[i] is a lower-case letter and s[i + 1] is the same letter but in upper-case or vice-versa.

To make the string good, you can choose two adjacent characters that make the string bad and remove them. You can keep doing this until the string becomes good.

Return the string after making it good. The answer is guaranteed to be unique under the given constraints.

Notice that an empty string is also good.

Example 1

Input: s = "leEeetcode"

Output: "leetcode"

Explanation: In the first step, either you choose i = 1 or i = 2, both will result "leEeetcode" to be reduced to "leetcode".

Example 2

Input: s = "abBAcC"

Output: ""

Explanation: We have many possible scenarios, and all lead to the same answer. For example:

"abBAcC" --> "aAcC" --> "cC" --> ""

"abBAcC" --> "abBA" --> "aA" --> ""

Example 3

Input: s = "s"

Output: "s"

Constraints

  • 1 <= s.length <= 100
  • s contains only lower and upper case English letters.

Solution (PHP 8.2)

function makeGood(string $string): string
{
    $charIndex = 0;
    while ($charIndex < \strlen($string)) {
        $charCurrent = \substr($string, $charIndex, length: 1);
        $charNext = \substr($string, offset: $charIndex + 1, length: 1);

        $isCharSame = 0 === \strcasecmp($charCurrent, $charNext);
        $isCaseSame = 0 === \strcmp($charCurrent, $charNext);

        if ($isCharSame && !$isCaseSame) {
            $string = \substr_replace($string, '', $charIndex, length: 2);

            if (0 !== $charIndex) {
                $charIndex--;
            }

            continue;
        }

        $charIndex++;
    }

    return $string;
}

Tests

Input stringResultTimeMemory
leEeetcodeleetcode65μs1440B
abBAcC29μs696B
ss37μs136B
lEeeetcodeleetcode63μs1440B
lEEeeeetcodeleetcode63μs1752B
39μs40B
OS: Ubuntu WSL2 (5.15.146.1-microsoft-standard-WSL2)
CPU: AMD Ryzen 7 5800X
RAM: 16GB

PHP 8.2.17 (cli) (built: Mar 16 2024 08:41:44) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.2.17, Copyright (c) Zend Technologies
    with Zend OPcache v8.2.17, Copyright (c), by Zend Technologies
    with Xdebug v3.3.1, Copyright (c) 2002-2023, by Derick Rethans

memory_limit => -1
xdebug.mode => profile

Code review (PHP 8.2)

function makeGood(string $string): string
{
    $charIndex = 0;
    while ($charIndex < \strlen($string)) {
        $charCurrent = \substr($string, $charIndex, length: 1);
        $charNext = \substr($string, offset: $charIndex + 1, length: 1);

-       $isCharSame = 0 === \strcasecmp($charCurrent, $charNext);
-       $isCaseSame = 0 === \strcmp($charCurrent, $charNext);

+       // Is not same character. e.g: `ab`, `aB` => `ab`, `Ba` => `ba`
+       if (0 !== \strcasecmp($charCurrent, $charNext)) {
+           $charIndex++;
+
+           continue;
+       }

-       if ($isCharSame && !$isCaseSame) {
+       // Is not same case. e.g: `aA`, `Aa`
+       if (0 !== \strcmp($charCurrent, $charNext)) {
            $string = \substr_replace($string, '', $charIndex, length: 2);

            if (0 !== $charIndex) {
                $charIndex--;
            }

            continue;
        }

        $charIndex++;
    }

    return $string;
}

Tests

Input stringResultTimeMemory
leEeetcodeleetcode57μs1184B
abBAcC28μs664B
ss35μs104B
lEeeetcodeleetcode54μs1184B
lEEeeeetcodeleetcode53μs1496B
11μs40B