My recursive never burst stack

When talking about algorithms,「递归」There is no way a skill,Because many algorithms actually use this technique to achieve.

那么问题来了,bad use of recursion「爆栈」️️️ StackOverFlow

but ! 「尾递归」不会爆栈！

So what are the characteristics of tail recursion compared to normal recursion?？

1. tail calling the function itself,No redundant calculation logic.
2. Optimize stack space,从O(n)到O(1)

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以 Python 为例,Mainly distinguish the use of stack space between ordinary recursion and tail recursion：

def recsum(x):
  if x == 1:
    return x
  else:
    return x + recsum(x - 1)

调用recsum(5)为例,The corresponding stack space changes are as follows：

recsum(5)
5 + recsum(4)
5 + (4 + recsum(3))
5 + (4 + (3 + recsum(2)))
5 + (4 + (3 + (2 + recsum(1))))
5 + (4 + (3 + (2 + 1)))
5 + (4 + (3 + 3))
5 + (4 + 6)
5 + 10
15

可观察,stack left to right,Increase to a peak and then calculate from right to left,This is often we don't want to.修改以上代码,can be tail recursive：

def tailrecsum(x, running_total=0):
  if x == 0:
    return running_total
  else:
    return tailrecsum(x - 1, running_total + x)

Compare the memory consumption of the latter tail recursion：

tailrecsum(5, 0) 
tailrecsum(4, 5) 
tailrecsum(3, 9)
tailrecsum(2, 12) 
tailrecsum(1, 14) 
tailrecsum(0, 15) 
15

ps : tailrecsum(4, 5) 执行的时候,tailrecsum(5, 0) It can actually be recycled on the stack..

You can see that tail recursion is compared to normal recursion,stack space does itO(1)的复杂度,It also plays a role in memory optimization..
then because it isO(1)复杂度,It's definitely not going to explode.

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