我在学校里很难理解递归。每当教授谈到它的时候,我似乎都懂了,但当我自己尝试的时候,它完全震撼了我的大脑。
我整晚都在尝试着解决《Towers of Hanoi》这款游戏,结果完全出乎我的意料。我的课本只有大约30页关于递归的内容,所以它不是很有用。有人知道哪些书籍或资源可以帮助澄清这个话题吗?
我在学校里很难理解递归。每当教授谈到它的时候,我似乎都懂了,但当我自己尝试的时候,它完全震撼了我的大脑。
我整晚都在尝试着解决《Towers of Hanoi》这款游戏,结果完全出乎我的意料。我的课本只有大约30页关于递归的内容,所以它不是很有用。有人知道哪些书籍或资源可以帮助澄清这个话题吗?
当前回答
Ouch. I tried to figure out the Towers of Hanoi last year. The tricky thing about TOH is it's not a simple example of recursion - you have nested recursions which also change the roles of towers on each call. The only way I could get it to make sense was to literally visualize the movement of the rings in my mind's eye, and verbalize what the recursive call would be. I would start with a single ring, then two, then three. I actually ordered the game on the internet. It took me maybe two or three days of cracking my brains to get it.
其他回答
递归函数就像弹簧,每次调用都要压缩一点。在每一步中,您将一些信息(当前上下文)放在堆栈上。当到达最后一步时,释放弹簧,立即收集所有值(上下文)!
不确定这个比喻是否有效…: -)
无论如何,除了经典的例子(阶乘是最糟糕的例子,因为它效率低,很容易被平化,Fibonacci, Hanoi…),这些都有点人为(我很少,如果有的话,在实际编程案例中使用它们),看看它真正被使用的地方是有趣的。
A very common case is to walk a tree (or a graph, but trees are more common, in general). For example, a folder hierarchy: to list the files, you iterate on them. If you find a sub-directory, the function listing the files call itself with the new folder as argument. When coming back from listing this new folder (and its sub-folders!), it resumes its context, to the next file (or folder). Another concrete case is when drawing a hierarchy of GUI components: it is common to have containers, like panes, to hold components which can be panes too, or compound components, etc. The painting routine calls recursively the paint function of each component, which calls the paint function of all the components it holds, etc.
不确定我是否很清楚,但我喜欢展示现实世界中教材的使用,因为这是我过去偶然发现的东西。
子函数隐式地使用递归,例如:
去迪士尼乐园自驾游
我们到了吗?(没有) 我们到了吗?(很快) 我们到了吗?(快了……) 我们到了吗? 我们到了吗?(!!!!!)
这时孩子就睡着了……
这个倒数函数是一个简单的例子:
倒计时()函数 { 返回(参数[0]> 0 ? ( Console.log(参数[0]),倒计时(参数[0]- 1)): “完成” ); } 倒计时(10);
霍夫施塔特定律也适用于软件项目。
The essence of human language is, according to Chomsky, the ability of finite brains to produce what he considers to be infinite grammars. By this he means not only that there is no upper limit on what we can say, but that there is no upper limit on the number of sentences our language has, there's no upper limit on the size of any particular sentence. Chomsky has claimed that the fundamental tool that underlies all of this creativity of human language is recursion: the ability for one phrase to reoccur inside another phrase of the same type. If I say "John's brother's house", I have a noun, "house", which occurs in a noun phrase, "brother's house", and that noun phrase occurs in another noun phrase, "John's brother's house". This makes a lot of sense, and it's an interesting property of human language.
参考文献
递归与人类思想
要理解递归,你只需要看看洗发水瓶上的标签:
function repeat()
{
rinse();
lather();
repeat();
}
这样做的问题是没有终止条件,递归将无限重复,或者直到洗发水或热水用完为止(外部终止条件,类似于吹你的堆栈)。
当使用递归解时,我总是尝试:
首先建立基本情况,即。 当n = 1的阶乘 试着想出一个一般的规则 对于其他情况
还有不同类型的递归解,分而治之的方法对分形和其他方法很有用。
如果你能先解决一些简单的问题,只是为了掌握窍门,这也会有帮助。一些例子是求解阶乘和生成第n个斐波那契数。
作为参考,我强烈推荐Robert Sedgewick的算法。
希望这能有所帮助。祝你好运。
要向一个六岁的孩子解释递归,首先要向一个五岁的孩子解释,然后再等一年。
实际上,这是一个有用的反例,因为递归调用应该更简单,而不是更难。向一个5岁的孩子解释递归就更难了,尽管你可以在0点停止递归,但你没有简单的解决方案来向一个0岁的孩子解释递归。
要使用递归解决一个问题,首先将其细分为一个或多个可以用相同方法解决的更简单的问题,然后当问题简单到无需进一步递归就可以解决时,您可以返回到更高的级别。
事实上,这是用递归方法来解决问题的递归定义。