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

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

 
 
  1. header (' content-type:text/html; CharSet = UTF -8 ');
  2. $ Str = implode (', Range (9, 0));
  3. print ' < p><strong>before reversed: strong>'. $str. '< / p> ';
  4. print ' < p> < strong>afterreversed: < /strong>'. Strrev ($str). ' < / P > ';
  5. /*
  6. The output is as follows:
  7. Before reversed:9876543210
  8. After reversed:0123456789
  9. */


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

 
 
  1. /**
  2. * Binary method for string reverse order
  3. * @param string $STR source strings
  4. * @return string returned in reverse order
  5. */
  6. function Reverse ($str=") {
  7. $ Len = strlen ($STR);//cannot use count or sizeof
  8. $ Mid = Floor ($len/2);
  9. For ($i=0; $i<$mid; $i + +) {
  10. $ Temp = $str [$i];
  11. $STR [$i] = $str [$len-$i-1];
  12. $str [$len-$i-1] = $temp;
  13. }
  14. return $str;
  15. }


2. Cyclic method

 
 
  1. /**
  2. * Cyclic implementation of strings in reverse order (efficiency is lower than dichotomy)
  3. * @param string $STR source strings
  4. * @return string returned in reverse order
  5. */
  6. function Reverse ($str=") {
  7. $ result = '' ;
  8. For ($i=1; $i<=strlen ($STR); $i + +) {
  9. $result . = substr ($str,-$i, 1);
  10. }
  11. return $result;
  12. }

3. Recursive method

 
 
  1. /**
  2. * Recursive implementation of strings in reverse order (inefficient)
  3. * @param string $STR source strings
  4. * @return string returned in reverse order
  5. */
  6. function Reverse ($str=") {
  7. Static $ result = '' ;
  8. /* Use the stack to understand recursive calls */
  9. if (strlen ($str) > 0) {
  10. Reverse (substr ($STR, 1));
  11. $result . = substr ($str, 0, 1);//The sentence must be placed after the previous statement
  12. }
  13. return $result;
  14. }

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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