How do i make a recursive function in python which does the following?-CodePudding

I've got an assignment in which I need to code a recursive function (with no loops) in python that returns: [[]] if n is 1 [[],[[]]] if n is 2 [[],[[]],[[],[[]]]] if n is 3 a pseudo code or a hint would be really appreciated my current code which im working on:

def ezr(n,a,b):
    a.append(b)
    b= deepcopy(a)
    return ezr(n-1,a,b)

def magic_list(n):
    return ezr(n,[],[])

ive got stuck with first function

CodePudding user response：

Generally recursion is the thing you should follow, but you have to work yourself on exit condition and how to receive data from recursion stack.

For now I see there are two problems, your recursion is infinite (wouldn't work for any call). Second is gathering data from your stack.

This should be enough to give you a lead to solve it on your own :)

from copy import deepcopy

def magic_list(n,a=[], b=[]):
    if n == 1:
        return []
    a = deepcopy(b)
    a.append(magic_list(n-1,a,b))
    return a

print(magic_list(1)) # []
print(magic_list(2)) # [[]]
print(magic_list(3)) # [[[]]]

If you strugle with visualization, use pythontutor.com

Visualization of execution step by step of code above: https://pythontutor.com/visualize.html#code= from copy import deepcopy def magic_list(n,a=[], b=[]): if n == 1: return [] a = deepcopy(b) a.append(magic_list(n-1,a,b)) return a print(magic_list(1)) # [] print(magic_list(2)) # [[]] print(magic_list(3)) # [[[]]] &cumulative=false&curInstr=0&heapPrimitives=nevernest&mode=display&origin=opt-frontend.js&py=3&rawInputLstJSON=[]&textReferences=false

CodePudding user response：

def magic_list(n, a=[]):
    a.append(a.copy())

    if n - 1:
        return magic_list(n - 1, a)
    else:
        return a

for n = 3:

print(magic_list(3))

Output:

[[], [[]], [[], [[]]]]

for n = 2:

print(magic_list(2))

Output:

[[], [[]]]

for n = 1:

print(magic_list(1))

Output:

[[]]