Leetcode

917. Reverse Only Letters

Given a string S, return the “reversed” string where all characters that are not a letter stay in the same place, and all letters reverse their positions.

 

Example 1:

Input: 

"ab-cd"

Output: 

"dc-ba"

Example 2:

Input: 

"a-bC-dEf-ghIj"

Output: 

"j-Ih-gfE-dCba"

Example 3:

Input: 

"Test1ng-Leet=code-Q!"

Output: 

"Qedo1ct-eeLg=ntse-T!"

 

Note:

  1. S.length <= 100
  2. 33 <= S[i].ASCIIcode <= 122
  3. S doesn’t contain \ or "

 

Straightforward solution. 

  1. collect letters in reverse order.
  2. go through string from beginning, if it’s letter, replace with letter from reverse string, else keep special chars and adjust pointer accordingly
  3. of course there’s space for improvement, but not necessary
<?php
class Solution {

    /**
     * @param String $S
     * @return String
     */
    function reverseOnlyLetters($S) {
        $x = '';
        $y = '';
        for($i = strlen($S)-1; $i >=0; $i -- ){
            if(ctype_alpha($S[$i])){
                $x .= $S[$i];
            }
        }
        $xi = 0;
        for($i = 0; $i < strlen($S); $i ++){
            if(!ctype_alpha($S[$i])){
                $y .= $S[$i];
            } else {
                $y .= $x[$xi];
                $xi ++;
            }
             
        }
        
        return $y;
    }
}

?>