遞歸函數(shù)
在函數(shù)內(nèi)部，可以調(diào)用其他函數(shù)。如果一個函數(shù)在內(nèi)部調(diào)用自身本身，這個函數(shù)就是遞歸函數(shù)。
舉個例子，我們來計(jì)算階乘 n! = 1 * 2 * 3 * ... * n，用函數(shù) fact(n)表示，可以看出：
fact(n) = n! = 1 * 2 * 3 * ... * (n-1) * n = (n-1)! * n = fact(n-1) * n
所以，fact(n)可以表示為 n * fact(n-1)，只有n=1時需要特殊處理。
于是，fact(n)用遞歸的方式寫出來就是：

def fact(n): if n==1:return 1 return n * fact(n - 1)

如果要計(jì)算2的n次方，那就是：

def fact(n): if n==1:return 1 return 2 * fact(n - 1)

?

我們可以修改一下代碼，詳細(xì)的列出每一步(注意打印出來的內(nèi)容的順序哦）：

def fact(n):print("factorial has been called with n = " + str(n))if n == 1:return 1else:res = n * fact(n - 1)print("intermediate result for ", n, " * fact(", n - 1, "): ", res)return resprint(fact(10))

結(jié)果是：

C:\Python35\python.exe C:/pylearn/bottlelearn/4.py factorial has been called with n = 10 factorial has been called with n = 9 factorial has been called with n = 8 factorial has been called with n = 7 factorial has been called with n = 6 factorial has been called with n = 5 factorial has been called with n = 4 factorial has been called with n = 3 factorial has been called with n = 2 factorial has been called with n = 1 intermediate result for 2 * fact( 1 ): 2 intermediate result for 3 * fact( 2 ): 6 intermediate result for 4 * fact( 3 ): 24 intermediate result for 5 * fact( 4 ): 120 intermediate result for 6 * fact( 5 ): 720 intermediate result for 7 * fact( 6 ): 5040 intermediate result for 8 * fact( 7 ): 40320 intermediate result for 9 * fact( 8 ): 362880 intermediate result for 10 * fact( 9 ): 3628800 1814400000Process finished with exit code 0

進(jìn)一步思考，如果，我們想實(shí)現(xiàn)遞歸的效果，但是，卻不想用到遞歸，在python怎么實(shí)現(xiàn)呢：

def fact(n):result=1for i in range(2,n+1):result=result*ireturn resultprint(fact(1)) print(fact(2)) print(fact(10))

?

轉(zhuǎn)載于:https://www.cnblogs.com/aomi/p/7047341.html

總結(jié)

以上是生活随笔為你收集整理的python的递归算法学习（1）的全部內(nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯，歡迎將生活随笔推薦給好友。