Factorization using tail recursion

Usually, when calculating the factorial of a number, we will use the recursive algorithm. The recursive book program calls itself, and has boundary conditions, forward segment and return segment.

The idea of recursion can be used in many scenarios. For example, I used recursion to parse XML before. If you want to calculate the factorial of an integer now, the general recursive method is as follows:

If tail recursion is used, it is in the following form:

If all recursive calls in a function appear at the end of the function, we call the recursive function tail recursive. When a recursive call is the last executed statement in the whole function body and its return value does not belong to a part of the expression, the recursive call is tail recursion.