Interpreting three methods of reverse permutation except PHP function Strrev () _php Tutorial

We are using

For the reverse order of strings, the PHP function Strrev () has the following test code:

 
 

  
  

  
header (' content-type:text/html; CharSet = UTF -8 '); 
  
  

  
$ Str  =  implode (', Range (9, 0)); 
  
  

  
print ' <   p><strong>before reversed:    strong>'. $str. '< / p> ';  
  
  

  
print ' <   p> <  strong>afterreversed:  <  /strong>'. Strrev ($str). ' < / P > '; 
  
  

  
/*
  
  

  
The output is as follows:
  
  

  
Before reversed:9876543210
  
  

  
After reversed:0123456789
  
  

  
*/
 
 

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

1. Dichotomy

 
 

  
  

  
/**
  
  

  
* Binary method for string reverse order
  
  

  
* @param string $STR source strings
  
  

  
* @return string returned in reverse order
  
  

  
*/
  
  

  
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

 
 

  
  

  
/**
  
  

  
* Cyclic implementation of strings in reverse order (efficiency is lower than dichotomy)
  
  

  
* @param string $STR source strings
  
  

  
* @return string returned in 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 source strings
  
  

  
* @return string returned in reverse order
  
  

  
*/
  
  

  
function Reverse ($str=") {
  
  

  
Static $ result  =  '' ; 
  
  

  
/* Use the stack to understand recursive calls */
  
  

  
if (strlen ($str)  >  0) {
  
  

  
Reverse (substr ($STR, 1));
  
  

  
$result . =  substr ($str, 0, 1);//The sentence must be placed after the previous statement
  
  

  
}
  
  

  
return $result;
  
  

  
}
 
 

This is the specific use of PHP function Strrev (), as well as three other ways to implement the reverse order.

http://www.bkjia.com/PHPjc/446151.html www.bkjia.com true http://www.bkjia.com/PHPjc/446151.html techarticle we are using the reverse order of the string, PHP function Strrev () The test code is as follows: Header (' content-type:text/html; charset = Utf-8 '); $ str = implode (", Range ( 9,0)); Prin ...

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