PHP还是比较常用的，于是我研究了一下PHP递归算法，在这里拿出来和大家分享一下，希望对大家有用。PHP，一个嵌套的缩写名称，是英文超级文本预处理语言（PHP:Hypertext Preprocessor）的缩写。PHP 是一种 HTML 内嵌式的语言，是一种在服务器端执行的嵌入HTML文档的脚本语言，语言的风格有类似于C语言，现在被很多的网站编程人员广泛的运用。PHP 独特的语法混合了 C、Java、Perl 以及 PHP 自创新的语法。
它可以比 CGI 或者 Perl 更快速的执行动态网页。用PHP做出的动态页面与其他的编程语言相比，PHP是将程序嵌入到HTML文档中去执行，执行效率比完全生成HTML标记的CGI要高许多；与同样是嵌入HTML文档的脚本语言JavaScript相比，PHP在服务器端执行，充分利用了服务器的性能；PHP执行引擎还会将用户经常访问的PHP程序驻留在内存中，其他用户再一次访问这个程序时就不需要重新编译程序了，只要直接执行内存中的代码就可以了，这也是PHP高效率的体现之一。
PHP具有非常强大的功能，所有的CGI或者JavaScript的功能PHP都能实现，而且支持几乎所有流行的数据库以及操作系统。我们这里详细的介绍一下PHP递归算法。
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PHP递归算法代码：
<ol class="dp-xml"><li class="alt"><span><span class="tag"><?</span><span class="tag-name">php</span><span> </span></span></li><li class=""><span>//定义PI一分的角度的值 </span></li><li class="alt"><span>define("PII",M_PI/180); </span></li><li class=""><span> </span></li><li class="alt"><span>//新建图像资源，并定义其背景为白色，前景色为黑色 </span></li><li class=""><span>$</span><span class="attribute">im</span><span>=</span><span class="attribute-value">imagecreate</span><span>(670,500); </span></li><li class="alt"><span>$</span><span class="attribute">white</span><span>=</span><span class="attribute-value">imagecolorallocate</span><span>($im,0xFF,0xFF,0xFF); </span></li><li class=""><span>$</span><span class="attribute">g</span><span>=</span><span class="attribute-value">imagecolorallocate</span><span>($im,0x00,0x00,0x00); </span></li><li class="alt"><span> </span></li><li class=""><span>//从下面实例化的代码可以得知，初始值$x,$y,$L,$a别分为300,500,100,270 </span></li><li class="alt"><span>functiondrawLeaf($g,$x,$y,$L,$a){ </span></li><li class=""><span>global$im; </span></li><li class="alt"><span>$</span><span class="attribute">B</span><span>=</span><span class="attribute-value">50</span><span>; </span></li><li class=""><span>$</span><span class="attribute">C</span><span>=</span><span class="attribute-value">9</span><span>; </span></li><li class="alt"><span>$</span><span class="attribute">s1</span><span>=</span><span class="attribute-value">2</span><span>; </span></li><li class=""><span>$</span><span class="attribute">s2</span><span>=</span><span class="attribute-value">3</span><span>; </span></li><li class="alt"><span>$</span><span class="attribute">s3</span><span>=</span><span class="attribute-value">1</span><span>.2; </span></li><li class=""><span>if($L</span><span class="tag">></span><span>$s1){ </span></li><li class="alt"><span>//计算叶子的定位上面 </span></li><li class=""><span>$</span><span class="attribute">x2</span><span>=$x+$L*cos($a*PII); </span></li><li class="alt"><span>$</span><span class="attribute">y2</span><span>=$y+$L*sin($a*PII); </span></li><li class=""><span>$</span><span class="attribute">x2R</span><span>=$x2+$L/$s2*cos(($a+$B)*PII); </span></li><li class="alt"><span>$</span><span class="attribute">y2R</span><span>=$y2+$L/$s2*sin(($a+$B)*PII); </span></li><li class=""><span>$</span><span class="attribute">x2L</span><span>=$x2+$L/$s2*cos(($a-$B)*PII); </span></li><li class="alt"><span>$</span><span class="attribute">y2L</span><span>=$y2+$L/$s2*sin(($a-$B)*PII); </span></li><li class=""><span> </span></li><li class="alt"><span>//计算叶子的定位下面 </span></li><li class=""><span>$</span><span class="attribute">x1</span><span>=$x+$L/$s2*cos($a*PII); </span></li><li class="alt"><span>$</span><span class="attribute">y1</span><span>=$y+$L/$s2*sin($a*PII); </span></li><li class=""><span>$</span><span class="attribute">x1L</span><span>=$x1+$L/$s2*cos(($a-$B)*PII); </span></li><li class="alt"><span>$</span><span class="attribute">y1L</span><span>=$y1+$L/$s2*sin(($a-$B)*PII); </span></li><li class=""><span>$</span><span class="attribute">x1R</span><span>=$x1+$L/$s2*cos(($a+$B)*PII); </span></li><li class="alt"><span>$</span><span class="attribute">y1R</span><span>=$y1+$L/$s2*sin(($a+$B)*PII); </span></li><li class=""><span> </span></li><li class="alt"><span>//别分画叶子的主干以及叶面 </span></li><li class=""><span>ImageLine($im,(int)$x,(int)$y,(int)$x2,(int)$y2,$g); </span></li><li class="alt"><span>ImageLine($im,(int)$x2,(int)$y2,(int)$x2R,(int)$y2R,$g); </span></li><li class=""><span>ImageLine($im,(int)$x2,(int)$y2,(int)$x2L,(int)$y2L,$g); </span></li><li class="alt"><span>ImageLine($im,(int)$x1,(int)$y1,(int)$x1L,(int)$y1L,$g); </span></li><li class=""><span>ImageLine($im,(int)$x1,(int)$y1,(int)$x1R,(int)$y1R,$g); </span></li><li class="alt"><span> </span></li><li class=""><span>//再次递归调用本身 </span></li><li class="alt"><span>drawLeaf($g,$x2,$y2,$L/$s3,$a+$C); </span></li><li class=""><span>drawLeaf($g,$x2R,$y2R,$L/$s2,$a+$B); </span></li><li class="alt"><span>drawLeaf($g,$x2L,$y2L,$L/$s2,$a-$B); </span></li><li class=""><span>drawLeaf($g,$x1L,$y1L,$L/$s2,$a-$B); </span></li><li class="alt"><span>drawLeaf($g,$x1R,$y1R,$L/$s2,$a+$B); </span></li><li class=""><span>} </span></li><li class="alt"><span>} </span></li><li class=""><span> </span></li><li class="alt"><span>//实例化 </span></li><li class=""><span>drawLeaf($g,300,500,100,270); </span></li><li class="alt"><span>header("Content-type:image/png"); </span></li><li class=""><span>imagepng($im); </span></li><li class="alt"><span></span><span class="tag">?></span><span>在我个人的PHP编程经验中，递归调用常常与静态变量使用。静态变量的含义可以参考PHP手册。希望下面的代码，会更有利于对递归以及静态变量的理解 </span></li><li class=""><span> </span></li><li class="alt"><span>header("Content-type:text/plain"); </span></li><li class=""><span>functionstatic_function(){ </span></li><li class="alt"><span>static$</span><span class="attribute">i</span><span>=</span><span class="attribute-value">0</span><span>; </span></li><li class=""><span>if($i++</span><span class="tag"><</span><span class="tag-name">10</span><span>){ </span></li><li class="alt"><span>echo$i."n"; </span></li><li class=""><span>static_function(); </span></li><li class="alt"><span>} </span></li><li class=""><span>} </span></li><li class="alt"><span>static_function(); </span></li></ol>这段代码会如数输出1到10的数字。在static_function函数第二次运行时，变量i由于是静态变量，所以仍被保留不被释放，进而可以得到自增的值。
