Php to change string without using loops or built-in functions

Question

How would you write a short php function to modify a string. The function should:

• have only one argument
• do not use the built-in function strrev or array_reverse
• Do not use a loop construct such as for, foreach, or while.

Answer 1

Quick scan, it all takes so long!

function rev($str) { return $str?rev(substr($str,1)).$str[0]:''; } 

Recursive, obviously, doesn't work with strings longer than 100 characters.

Answer 2

Since this sounds like a question about homework, I'll tell you how, but you code it yourself. Turn the string into a cast array. Then use one of the array sorting functions, which performs a user-defined sorting function.

Answer 3

 function reverseString($string) { return shell_exec(sprintf('ruby -e \'puts "%s".reverse\'', preg_replace("/\"/", "\\\"", $string))); } 

Answer 4

Recursive solution:

 function sr( $txt ){ return $txt[ strlen( $txt ) - 1 ] . ( ( strlen( $txt ) > 1 )?sr( substr( $txt, 0, strlen($txt)-1 ) ):null) ; } echo sr( "abc def ghi jklm" ); 

Explanation:

 return $txt[ strlen( $txt ) - 1 ] // return last byte of string . // concatenate it with: (( strlen( $txt ) > 1 ) ? // if there are more bytes in string sr( substr( $txt, 0, strlen( $txt ) - 1 ) // then with reversed string without last letter : null ); // otherwise with null 

To make it work with a null string, another conditional expression was added:

 return (strlen($txt))? ($txt[ strlen( $txt ) - 1 ] . ( ( strlen( $txt ) > 1 )?sr( substr( $txt, 0, strlen($txt)-1 ) ):null)):"" ; 

Answer 5

  <?php // Reversed string and Number // For Example : $str = "hello world. This is john duvey"; $number = 123456789; $newStr = strrev($str); $newBum = strrev($number); echo $newStr; echo "<br />"; echo $newBum; OUTPUT : first : yevud nhoj si sihT .dlrow olleh second: 987654321`enter code here` 

Answer 6

Meets all your requirements, but works only in PHP 5.3 or higher. To do his work on others is left as homework.

 function reverse($str) { $i=0; $j=strlen($str)-1; start: if($i>=$j) { goto done; } $tmp = $str[$j]; $str[$j--] = $str[$i]; $str[$i++] = $tmp; goto start; done: return $str; } 

Answer 7

 function reverse_string($string) { if($string !== '') return substr($string, -1).reverse_string(substr($string, 0, strlen($string)-2)); } 

Answer 8

Recursive solution. Feels like this is what your teacher is looking for.

 function my_strrev ($str) { $length = strlen($str); switch ($length) { case 0: return ''; case 1: return $str; break; case 2: return $str[1] . $str[0]; default : return $str[$length-1] . my_strrev(substr($str,1,-1)) . $str[0]; break; } } 

It changes the first and last letters and does the same with the rest of the line.

Update: Inspired by mateusza, I created another solution (its fun;))

 function my_strrev2 ($str) { return $str ? my_strrev2(substr($str, 1)) . $str[0] : ''; } 

It works similarly to mateuszas, but this one adds the first character, not the last one.

Answer 9

My answer is OOP and uses recursion. Carefully refers to the recursion limit.

 class StringReverser { public $reversed_string; public function __construct ($string) { $original_recursion_limit = ini_get('pcre.recursion_limit'); $array = str_split($string); krsort($array); $i = strlen($string); ini_set('pcre.recursion_limit', $i+1); $this->add2string($string, $i, $array); ini_set('pcre.recursion_limit', $original_recursion_limit); } public function reverse() { return $this->reversed_string; } private function add2string ($s, $i, $a) { if($i) { $i--; $this->reversed_string .= $a[$i]; $this->add2string($s, $i,$a, $this->reversed_string); } } } $string = "Elzo Valugi"; echo $string ."<br>"; $reverser = new StringReverser($string); echo $reverser->reverse(); 

Answer 10

 <?php $string="jomon is name my"; for($i=strlen($string);$i>=0;$i--) { $char.=$string{$i}; } echo $char."<br/>"; for($i=0; $i<strlen($char);$i++) { if($char[$i+1]==" " || $char[$i+1]=="") { for($temp=$i; $temp>=0 && $char[$temp]!=' '; $temp--) echo $char[$temp]; } echo " "; } ?>