# PHP bubble algorithm (Recursive Implementation) and bubble Recursion

Source: Internet
Author: User

PHP bubble algorithm (Recursive Implementation) and bubble Recursion

Implementation

Copy codeThe Code is as follows:
/*
Bubble algorithm (Recursive Implementation)
*/

Function maoPao (\$ array, \$ index = 0)
{
\$ Count = count (\$ array );
If (\$ count-1) <= \$ index)
Return \$ array;

For (\$ I = \$ count-1; \$ I> \$ index; \$ I --)
{
If (\$ array [\$ I] <\$ array [\$ I-1])
{
\$ Tmp = \$ array [\$ I];
\$ Array [\$ I] = \$ array [\$ I-1];
\$ Array [\$ I-1] = \$ tmp;
}
}
\$ Index ++;
Return maoPao (\$ array, \$ index );
// Return maoPao (\$ array, \$ index ++ );
}

\$ Arr = array (12, 4, 3, 1, 9, 5, 6, 8, 7 );
Var_dump (maoPao (\$ arr ));

Result:

Copy codeThe Code is as follows:
Array ( => 1  => 3  => 4  => 5  => 6  => 7  => 8  => 9  => 12)

Problem:

When trying this implementation, I encountered a problem that has not yet been solved.
Here:

Copy codeThe Code is as follows:
\$ Index ++;
Return maoPao (\$ array, \$ index );
// Return maoPao (\$ array, \$ index ++ );

/******************
If you use the third row directly, instead of \$ index ++, and then ruturn, it will enter an endless loop. I output \$ index at the beginning of the function, all of which are 0, that is to say, the parameter passed to the recursive function after \$ index ++ is not the result of \$ index ++ (that is, \$ index = \$ index + 1 ).
MaoPao (\$ array, \$ index ++) is not a brief description of \$ index ++; return maoPao (\$ array, \$ index);. Why are the two results different, I hope you can answer this question.
******************/

Supplement:

Copy codeThe Code is as follows:
The difference between \$ index ++ and ++ \$ index is that \$ index ++ is called post increment and ++ \$ index is called pre increment, although the final \$ index result will all be + 1. However, when variables are passed, they may be different.

\$ Index = 1;
\$ M = \$ index ++;
Echo \$ index. '<br/>'; // The result is 2.
Echo \$ m. '<br/>'; // The result is 1. because it is post-increment, the initial \$ index = 1 is first assigned to \$ m, and then \$ index increases by 1;

\$ Index = 1;
\$ N = ++ \$ index;
Echo \$ index. '<br/>'; // The result is 2.
Echo \$ n; // The result is 2. Because it is a previous increment, \$ index + 1 is executed first, and then assigned to \$ n;

This may not be easy to remember, so you must pay attention when using it. In the above problem, I ignored this problem and caused the infinite 0 value passed by \$ index to lock the recursion.

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