php递归问题
- PHP code
<!-- Code highlighting produced by Actipro CodeHighlighter (freeware) http://www.CodeHighlighter.com/ --> function test($a) { echo ' '.$a.' '; if($a >0) { test($a-1); }else { echo ''; } echo '<b>'.$a.'</b>'; } test(3)
3 2 1 0 0 1 2 3
各位大侠给解释下运行步骤,或者点参考资料让我去研究下,本人菜鸟。多多包涵
------解决方案--------------------
兄弟,一言难尽了,调用一函数,就得开辟一新栈,递归调用test($a-1)完时,已经输出了3 2 1 0 这个明白不?
然后接着当然是这玩意了,是吧, 明白吗?
最后回收开辟的栈,都要执行这玩意echo ''.$a.''; ~~~
哪里看不明白,指出,尽我所能给你仔细讲解哈~~
------解决方案--------------------
每一层都一样:
1,打印$a
2,进入下一层递归 or 打印
3, 打印$a
那么就是:
打印3, 打印2, 打印1, 打印0, 打印,打印0, 打印1, 打印2, 打印3。
红色是步骤1,蓝色是步骤2.
------解决方案--------------------
test(3) 执行function test :
1. echo $a = 3 然后进入if判断 3>0 执行 test(2) ;这里函数test(3) 还没有执行完的。是先去执行了 test(2) ------- *1;
2. test(2) echo $a = 2 然后判断2>0 执行 test(1) ; 这里也是test(2) 还没有执行完。先去执行了 test(1) ------------*2;
3.test(1) echo $a = 1; 然后判断1>0 执行 test(0) ;这里test(1) 还没有执行完。先去执行了test(0) -----------*3;
4. test(0) echo $a = 0 ;然后判断 0>0 执行了echo echo 0;
5. 4执行完后回到了 *3 ,判断完了后执行 echo $a = 1;
6. 5执行完 回到 * 2 echo $a = 2;
7. 6执行完 回到 *1 echo $a = 3;
这是 一层一层的深入 然后又是一层一层的往外走。

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