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| 1 | +def rotate_array(arr: list[int], steps: int) -> list[int]: |
| 2 | + """ |
| 3 | + Rotates a list to the right by steps positions. |
| 4 | +
|
| 5 | + Parameters: |
| 6 | + arr (List[int]): The list of integers to rotate. |
| 7 | + steps (int): Number of positions to rotate. Can be negative for left rotation. |
| 8 | +
|
| 9 | + Returns: |
| 10 | + List[int]: Rotated list. |
| 11 | +
|
| 12 | + Examples: |
| 13 | + >>> rotate_array([1, 2, 3, 4, 5], 2) |
| 14 | + [4, 5, 1, 2, 3] |
| 15 | + >>> rotate_array([1, 2, 3, 4, 5], -2) |
| 16 | + [3, 4, 5, 1, 2] |
| 17 | + >>> rotate_array([1, 2, 3, 4, 5], 7) |
| 18 | + [4, 5, 1, 2, 3] |
| 19 | + >>> rotate_array([], 3) |
| 20 | + [] |
| 21 | + """ |
| 22 | + |
| 23 | + n = len(arr) |
| 24 | + if n == 0: |
| 25 | + return arr |
| 26 | + |
| 27 | + steps = steps % n |
| 28 | + |
| 29 | + if steps < 0: |
| 30 | + steps += n |
| 31 | + |
| 32 | + def reverse(start: int, end: int) -> None: |
| 33 | + """ |
| 34 | + Reverses a portion of the list in place from index start to end. |
| 35 | +
|
| 36 | + Parameters: |
| 37 | + start (int): Starting index of the portion to reverse. |
| 38 | + end (int): Ending index of the portion to reverse. |
| 39 | +
|
| 40 | + Returns: |
| 41 | + None |
| 42 | +
|
| 43 | + Examples: |
| 44 | + >>> example = [1, 2, 3, 4, 5] |
| 45 | + >>> def reverse_test(arr, start, end): |
| 46 | + ... while start < end: |
| 47 | + ... arr[start], arr[end] = arr[end], arr[start] |
| 48 | + ... start += 1 |
| 49 | + ... end -= 1 |
| 50 | + >>> reverse_test(example, 0, 2) |
| 51 | + >>> example |
| 52 | + [3, 2, 1, 4, 5] |
| 53 | + >>> reverse_test(example, 2, 4) |
| 54 | + >>> example |
| 55 | + [3, 2, 5, 4, 1] |
| 56 | + """ |
| 57 | + |
| 58 | + while start < end: |
| 59 | + arr[start], arr[end] = arr[end], arr[start] |
| 60 | + start += 1 |
| 61 | + end -= 1 |
| 62 | + |
| 63 | + reverse(0, n - 1) |
| 64 | + reverse(0, steps - 1) |
| 65 | + reverse(steps, n - 1) |
| 66 | + |
| 67 | + return arr |
| 68 | + |
| 69 | + |
| 70 | +if __name__ == "__main__": |
| 71 | + examples = [ |
| 72 | + ([1, 2, 3, 4, 5], 2), |
| 73 | + ([1, 2, 3, 4, 5], -2), |
| 74 | + ([1, 2, 3, 4, 5], 7), |
| 75 | + ([], 3), |
| 76 | + ] |
| 77 | + |
| 78 | + for arr, steps in examples: |
| 79 | + rotated = rotate_array(arr.copy(), steps) |
| 80 | + print(f"Rotate {arr} by {steps}: {rotated}") |
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