Rotating a list without using collection.deque

Question

I want to make a script. The program should get some list L with values, and natural number N.
If N>0, the list's objects move N steps to left.
If N<0, the list's objects move abs(N) to the right.
If N=0 the list remain the same...

For example: For N=1 and L=[1,2,3,4,5], the output is [2,3,4,5,1].
For same list and N=-1 the output is [5,1,2,3,4]

I actually did it using collection.deque, but I want to do this with nothing but lists, for loop and 'if'.

I have problem to understand how to make the objects move.

l = input("enter list:")
N = input("enter number of rotations:")
import collections
d = collections.deque(l)
d.rotate(-N)
print d

Answer 1

You can use list slicing:

def rotate(L, N):
    if not L or N % len(L) == 0:
        return L
    return L[N % len(L):] + L[:N % len(L)]

L = [1, 2, 3, 4, 5]

for N in range(-3, 4):
    print(rotate(L, N))

Output:

[3, 4, 5, 1, 2]
[4, 5, 1, 2, 3]
[5, 1, 2, 3, 4]
[1, 2, 3, 4, 5]
[2, 3, 4, 5, 1]
[3, 4, 5, 1, 2]
[4, 5, 1, 2, 3]

Note that if you use a list, the time complexity of a rotation is linear to the number of elements in the list in general, since you have to move all existing elements. deque.rotate(), on the other hand, is O(k), with k being the number of steps. Therefore, if you need to rotate more than once deque.rotate() is the way to go.