how to reduce memory usage this program recursive

Question

This function return array of number n digit but it use memory very much. How can I improve this func for reduce memory

def think(n=5):
    if n == 1:
        return ([str(i) for i in range(1,10)])
    else :
        result = []
        # result1 = think(n-1)
        for i in think(n-1):
            for j in range(10):
                result.append(i+str(j))
        return result

Answer 1

You can start by removing the result list out of recursion. Because for every recursive call you are creating a new result list. Instead, you should create it once before calling the recursive function and keep passing it as function parameter.