How to implement PHP string in reverse order

Source: Internet
Author: User
Tags string back
This article mainly introduced the PHP string in reverse order implementation method, combined with the example form summarizes and analyzes the Strrev function, the dichotomy method, the cyclic method, recursive method and so on commonly used string reverse arrangement operation Realization Skill, needs the friend to refer to the next

Specific as follows:

The simplest test code for using the PHP function, Strrev (), is in reverse order of the string:

Header (' content-type:text/html; Charset=utf-8 '); $str = Implode (", Range (9, 0));p rint ' < P><strong>before Reversed: </strong> '. $str. ' </p> ';p rint ' < p>< Strong>after reversed: </strong> '. Strrev ($STR). ' </p> ';/* output is as follows: Before Reversed:9876543210after reversed:0123456789*/

What if we don't use the built-in PHP function Strrev ()? There are 3 different methods (dichotomy, cyclic, recursive), but no performance tests are performed.

1. Dichotomy

/*** binary method to implement strings in reverse order * @param string $STR The source string * @return string returns the inverse of the strings */function reverse ($str = ") {  $len = strlen ($STR);  //cannot use count or sizeof  $mid = Floor ($len/2);  for ($i =0; $i < $mid; $i + +) {    $temp = $str [$i];    $STR [$i] = $str [$len-$i-1];    $str [$len-$i-1] = $temp;  }  return $STR;}

2. Cyclic method

The/*** loop implements an inverse arrangement of strings (less efficient than dichotomy) * @param string $STR The source string * @return string returns the strings after reverse order */function reverse ($str = ") {  $result = '';  for ($i =1; $i <=strlen ($STR), $i + +) {    $result. = substr ($str,-$i, 1);  }  return $result;}

3. Recursive method

/*** recursive implementation of strings in reverse order (inefficient) * @param string $STR The source string * @return string back to reverse the strings */function reverse ($str = ") {  static $resul t = ';  /* Use the stack to understand recursive calls */  if (strlen ($STR) > 0) {    reverse (substr ($STR, 1));    $result. = substr ($str, 0, 1);    This sentence must be placed after the previous statement  }  return $result;}

The above is the whole content of this article, I hope that everyone's study has helped.


Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.