rotate.py

def rotate_left_1(A):
    "rotate in place once to the left (as if k = 1)"
    for i in range(len(A) - 1):
        A[i], A[i + 1] = A[i + 1], A[i]


def rotate_right_1(A):
    "rotate in place once to the right (as if k = -1)"
    for i in range(len(A) - 1):
        A[i], A[i - 1] = A[i - 1], A[i]


def rotate(A, k):
    "rotate in place k times to the left"
    k = k % len(A)
    for _ in range(k):
        if k > 0:
            rotate_left_1(A)
        else:
            rotate_right_1(A)


if __name__ == "__main__":
    # example table of rotations
    print("list, k")
    for i in [0, 1, 2, 3, 4, -1, -2, -3, -4, 400]:
        A = list("ABCD")
        rotate(A, i)
        print("".join(A), i)

"""
list, k
ABCD 0
BCDA 1
CDAB 2
DABC 3
ABCD 4
DABC -1
CDAB -2
BCDA -3
ABCD -4
ABCD 400
"""