diff --git a/data_structures/arrays/rotate_array.py b/data_structures/arrays/rotate_array.py new file mode 100644 index 000000000000..d5ce4b4078b3 --- /dev/null +++ b/data_structures/arrays/rotate_array.py @@ -0,0 +1,80 @@ +def rotate_array(arr: list[int], steps: int) -> list[int]: + """ + Rotates a list to the right by steps positions. + + Parameters: + arr (List[int]): The list of integers to rotate. + steps (int): Number of positions to rotate. Can be negative for left rotation. + + Returns: + List[int]: Rotated list. + + Examples: + >>> rotate_array([1, 2, 3, 4, 5], 2) + [4, 5, 1, 2, 3] + >>> rotate_array([1, 2, 3, 4, 5], -2) + [3, 4, 5, 1, 2] + >>> rotate_array([1, 2, 3, 4, 5], 7) + [4, 5, 1, 2, 3] + >>> rotate_array([], 3) + [] + """ + + n = len(arr) + if n == 0: + return arr + + steps = steps % n + + if steps < 0: + steps += n + + def reverse(start: int, end: int) -> None: + """ + Reverses a portion of the list in place from index start to end. + + Parameters: + start (int): Starting index of the portion to reverse. + end (int): Ending index of the portion to reverse. + + Returns: + None + + Examples: + >>> example = [1, 2, 3, 4, 5] + >>> def reverse_test(arr, start, end): + ... while start < end: + ... arr[start], arr[end] = arr[end], arr[start] + ... start += 1 + ... end -= 1 + >>> reverse_test(example, 0, 2) + >>> example + [3, 2, 1, 4, 5] + >>> reverse_test(example, 2, 4) + >>> example + [3, 2, 5, 4, 1] + """ + + while start < end: + arr[start], arr[end] = arr[end], arr[start] + start += 1 + end -= 1 + + reverse(0, n - 1) + reverse(0, steps - 1) + reverse(steps, n - 1) + + return arr + + +if __name__ == "__main__": + examples = [ + ([1, 2, 3, 4, 5], 2), + ([1, 2, 3, 4, 5], -2), + ([1, 2, 3, 4, 5], 7), + ([], 3), + ] + + for arr, steps in examples: + rotated = rotate_array(arr.copy(), steps) + print(f"Rotate {arr} by {steps}: {rotated}")