我试图打印出阶乘递归函数的执行流程。
def factorial(n):
space=' '*(4*n)
print(space,'factorial ',n)
if n==0:
print(space,'returning 1')
return 1
else:
recurse=factorial(n-1)
result=n*recurse
print(space,'returning ', result)
return n*recurse
使用factorial(2)结果将是正确的:
factorial 2
factorial 1
factorial 0
returning 1
returning 1
returning 2
2
但是当我不使用变量recurse = factorial(n-1)时:
def factorial(n):
space=' '*(4*n)
print(space,'factorial ',n)
if n==0:
print(space,'returning 1')
return 1
else:
result=n*factorial(n-1)
print(space,'returning ', result)
return n*factorial(n-1)
然后用factorial(2)打印出不同的流程:
factorial 2
factorial 1
factorial 0
returning 1
returning 1
factorial 0
returning 1
returning 2
factorial 1
factorial 0
returning 1
returning 1
factorial 0
returning 1
2
我的问题是:为什么有不同的执行流程[有和没有变量recurse = factorial(n-1)]?
这是由于您的代码中有以下额外的函数调用
def factorial(n):
space=' '*(4*n)
print(space,'factorial ',n)
if n==0:
print(space,'returning 1')
return 1
else:
result=n*factorial(n-1)
print(space,'returning ', result)
return n*factorial(n-1) # factorial(n-1) is called second time so that this function is executed once again
您可以执行以下类似的执行操作
def factorial(n):
space=' '*(4*n)
print(space,'factorial ',n)
if n==0:
print(space,'returning 1')
return 1
else:
result=n*factorial(n-1)
print(space,'returning ', result)
return result