I have been having a look at some simple recursive functions to wrap my head around the concept. However one example has me a little confused.

The function below uses recursion to obtain the largest integer from a list:

A = [-4, 2, 4]
n = len(A)
def findMaxRec(A, n):
    if (n == 1):
        return A[0]
    else:
        return max(A[n - 1], findMaxRec(A, n - 1))

As n will eventually equal 1 why does the function not always return the first element in the list?

CodePudding user response：

In such cases it might be helpful to just write out what code will be executed. I've tried to do that with your function as pseudo-code, where n is replaced with its value:

findMaxRec(A, 3):
    if (3 == 1):
        return A[0]
    else:
        return max(A[3 - 1], 
            findMaxRec(A, 2):
                if (2 == 1):
                    return A[0]
                else:
                    return max(A[2 - 1], 
                        findMaxRec(A, 1):
                            if (1 == 1):
                                return A[0]
                )
    )

Effectively, this results in:

max(A[2], max(A[1], A[0]))

Where the inner call max(A[1], A[0]) = max(2, -4) = 2

And the outer call max(A[2], ...) = max(4, 2) = 4