A detailed introduction to PHP recursive algorithms

PHP recursive algorithm code: Copy the code as follows: & lt ;? Php // define the point-of-PI angle value define (& quot; PII & quot;, M_PI/180); // create an image resource and define its background as white, the foreground color is black $ im = imagecreate (670,500); $ white = imagecolorallocate ($ im, 0xFF,

PHP recursive algorithm code:

Copy the code as follows:
<? Php
// Define the angle value of PI ("PII", M_PI/180 );
// Create an image resource and set the background to White. the foreground color to black.
$ Im = imagecreate (670,500 );
$ White = imagecolorallocate ($ im, 0xFF, 0xFF, 0xFF );
$ G = imagecolorallocate ($ im, 0x00,0x00,0x00 );
// The Code instantiated below shows that the initial values $ x, $ y, $ L, and $ a are not divided into 300,500,100,270.
FunctiondrawLeaf ($ g, $ x, $ y, $ L, $)
{Global $ im; $ B = 50; $ C = 9; $ s1 = 2; $ s2 = 3; $ s3 = 1.2;
If ($ L> $ s1 ){
// Calculate the leaf positioning above
$ X2 = $ x + $ L * cos ($ a * PII );
$ Y2 = $ y + $ L * sin ($ a * PII );
$ X2R = $ x2 + $ L/$ s2 * cos ($ a + $ B) * PII );
$ Y2R = $ y2 + $ L/$ s2 * sin ($ a + $ B) * PII );
$ X2L = $ x2 + $ L/$ s2 * cos ($ a-$ B) * PII );
$ Y2L = $ y2 + $ L/$ s2 * sin ($ a-$ B) * PII );
// Calculate the position of the leaf.
$ X1 = $ x + $ L/$ s2 * cos ($ a * PII );
$ Y1 = $ y + $ L/$ s2 * sin ($ a * PII );
$ X1L = $ x1 + $ L/$ s2 * cos ($ a-$ B) * PII );
$ Y1L = $ y1 + $ L/$ s2 * sin ($ a-$ B) * PII );
$ X1R = $ x1 + $ L/$ s2 * cos ($ a + $ B) * PII );
$ Y1R = $ y1 + $ L/$ s2 * sin ($ a + $ B) * PII );
// Separate the trunk and leaf area of the leaves
ImageLine ($ im, (int) $ x, (int) $ y, (int) $ x2, (int) $ y2, $ g );
ImageLine ($ im, (int) $ x2, (int) $ y2, (int) $ x2R, (int) $ y2R, $ g );
ImageLine ($ im, (int) $ x2, (int) $ y2, (int) $ x2L, (int) $ y2L, $ g );
ImageLine ($ im, (int) $ x1, (int) $ y1, (int) $ x1L, (int) $ y1L, $ g );
ImageLine ($ im, (int) $ x1, (int) $ y1, (int) $ x1R, (int) $ y1R, $ g );
// Re-recursive call itself
DrawLeaf ($ g, $ x2, $ y2, $ L/$ s3, $ a + $ C );
DrawLeaf ($ g, $ x2R, $ y2R, $ L/$ s2, $ a + $ B );
DrawLeaf ($ g, $ x2L, $ y2L, $ L/$ s2, $ a-$ B );
DrawLeaf ($ g, $ x1L, $ y1L, $ L/$ s2, $ a-$ B );
DrawLeaf ($ g, $ x1R, $ y1R, $ L/$ s2, $ a + $ B );
}
}
// Instantiate
DrawLeaf ($ g, 300,500,100,270 );
Header ("Content-type: image/png ");
Imagepng ($ im );
?>

In my personal PHP programming experience, recursive calls are often used with static variables. For more information about static variables, see The PHP Manual. We hope the following code will be more conducive to understanding PHP recursive algorithms and static variables.
Copy the code as follows:
Header ("Content-type: text/plain"); functionstatic_function ()
{
Static $ I = 0;
If ($ I ++ <10)
{
Echo $ I. "\ n ";
Static_function ();
}
}
Static_function ();

This PHP recursive algorithm code outputs numbers ranging from 1 to 10. During the second operation of the static_function, variable I is retained and cannot be released because it is a static variable, so that the auto-increment value can be obtained.