From d5b2f61ea084112760fcb8d8ec5ba22cb4f754b7 Mon Sep 17 00:00:00 2001 From: lucaCambi77 Date: Wed, 11 Oct 2023 03:35:10 +0200 Subject: [PATCH] BAEL-6913 - Rotate array in java (#14861) * feat: rotate array in java * fix: When to when --- .../algorithms/rotatearray/RotateArray.java | 102 ++++++++++++++ .../rotatearray/RotateArrayUnitTest.java | 124 ++++++++++++++++++ 2 files changed, 226 insertions(+) create mode 100644 algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/rotatearray/RotateArray.java create mode 100644 algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/rotatearray/RotateArrayUnitTest.java diff --git a/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/rotatearray/RotateArray.java b/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/rotatearray/RotateArray.java new file mode 100644 index 0000000000..36490d4899 --- /dev/null +++ b/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/rotatearray/RotateArray.java @@ -0,0 +1,102 @@ +package com.baeldung.algorithms.rotatearray; + +/** + * To speed up the rotation, we narrow k rotations to the remainder of k divided by the array length, or k module the array length. + * Therefore, a large rotation number will be translated into the relative smallest rotation. + * All solutions replace the original array, although they might use an extra array to compute the rotation. + */ +public class RotateArray { + + private RotateArray() { + throw new IllegalStateException("Rotate array algorithm utility methods class"); + } + + /** + * + * @param arr array to apply rotation to + * @param k number of rotations + */ + public static void bruteForce(int[] arr, int k) { + checkInvalidInput(arr, k); + + k %= arr.length; + int temp; + int previous; + for (int i = 0; i < k; i++) { + previous = arr[arr.length - 1]; + for (int j = 0; j < arr.length; j++) { + temp = arr[j]; + arr[j] = previous; + previous = temp; + } + } + } + + /** + * + * @param arr array to apply rotation to + * @param k number of rotations + */ + public static void withExtraArray(int[] arr, int k) { + checkInvalidInput(arr, k); + + int[] extraArray = new int[arr.length]; + for (int i = 0; i < arr.length; i++) { + extraArray[(i + k) % arr.length] = arr[i]; + } + System.arraycopy(extraArray, 0, arr, 0, arr.length); + } + + /** + * + * @param arr array to apply rotation to + * @param k number of rotations + */ + public static void cyclicReplacement(int[] arr, int k) { + checkInvalidInput(arr, k); + + k = k % arr.length; + int count = 0; + for (int start = 0; count < arr.length; start++) { + int current = start; + int prev = arr[start]; + do { + int next = (current + k) % arr.length; + int temp = arr[next]; + arr[next] = prev; + prev = temp; + current = next; + count++; + } while (start != current); + } + } + + /** + * + * @param arr array to apply rotation to + * @param k number of rotations + */ + public static void reverse(int[] arr, int k) { + checkInvalidInput(arr, k); + + k %= arr.length; + reverse(arr, 0, arr.length - 1); + reverse(arr, 0, k - 1); + reverse(arr, k, arr.length - 1); + } + + private static void reverse(int[] nums, int start, int end) { + while (start < end) { + int temp = nums[start]; + nums[start] = nums[end]; + nums[end] = temp; + start++; + end--; + } + } + + private static void checkInvalidInput(int[] arr, int rotation) { + if (rotation < 1 || arr == null) + throw new IllegalArgumentException("Rotation must be greater than zero or array must be not null"); + } +} diff --git a/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/rotatearray/RotateArrayUnitTest.java b/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/rotatearray/RotateArrayUnitTest.java new file mode 100644 index 0000000000..4a98acdb75 --- /dev/null +++ b/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/rotatearray/RotateArrayUnitTest.java @@ -0,0 +1,124 @@ +package com.baeldung.algorithms.rotatearray; + +import static com.baeldung.algorithms.rotatearray.RotateArray.bruteForce; +import static com.baeldung.algorithms.rotatearray.RotateArray.cyclicReplacement; +import static com.baeldung.algorithms.rotatearray.RotateArray.reverse; +import static com.baeldung.algorithms.rotatearray.RotateArray.withExtraArray; +import static org.junit.jupiter.api.Assertions.assertArrayEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import org.junit.jupiter.api.Test; + +class RotateArrayUnitTest { + + private final int[] arr = { 1, 2, 3, 4, 5, 6 }; + private final int rotationLtArrayLength = 1; + private final int rotationGtArrayLength = arr.length + 2; + private final int[] ltArrayLengthRotation = { 6, 1, 2, 3, 4, 5 }; + private final int[] gtArrayLengthRotation = { 5, 6, 1, 2, 3, 4 }; + + @Test + void givenInputArray_whenNoRotationOrEmptyArray_thenThrowIllegalArgumentException() { + final int noRotation = 0; + final int someRotation = arr.length - 1; + + assertThrows(IllegalArgumentException.class, () -> bruteForce(arr, noRotation)); + assertThrows(IllegalArgumentException.class, () -> withExtraArray(arr, noRotation)); + assertThrows(IllegalArgumentException.class, () -> cyclicReplacement(arr, noRotation)); + assertThrows(IllegalArgumentException.class, () -> reverse(arr, noRotation)); + + assertThrows(IllegalArgumentException.class, () -> bruteForce(null, someRotation)); + assertThrows(IllegalArgumentException.class, () -> withExtraArray(null, someRotation)); + assertThrows(IllegalArgumentException.class, () -> cyclicReplacement(null, someRotation)); + assertThrows(IllegalArgumentException.class, () -> reverse(null, someRotation)); + } + + @Test + void givenInputArray_whenUseBruteForceRotationLtArrayLength_thenRotateArrayOk() { + + bruteForce(arr, rotationLtArrayLength); + assertArrayEquals(ltArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseBruteForceRotationGtArrayLength_thenRotateArrayOk() { + + bruteForce(arr, rotationGtArrayLength); + assertArrayEquals(gtArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseBruteForceRotationEqArrayLength_thenDoNothing() { + int[] expected = arr.clone(); + + bruteForce(arr, arr.length); + assertArrayEquals(expected, arr); + } + + @Test + void givenInputArray_whenUseExtraArrayRotationLtArrayLength_thenRotateArrayOk() { + + withExtraArray(arr, rotationLtArrayLength); + assertArrayEquals(ltArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseExtraArrayRotationGtArrayLength_thenRotateArrayOk() { + + withExtraArray(arr, rotationGtArrayLength); + assertArrayEquals(gtArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseExtraArrayWithRotationEqArrayLength_thenDoNothing() { + int[] clone = arr.clone(); + + withExtraArray(arr, arr.length); + assertArrayEquals(clone, arr); + } + + @Test + void givenInputArray_whenUseCyclicReplacementRotationLtArrayLength_thenRotateArrayOk() { + + cyclicReplacement(arr, rotationLtArrayLength); + assertArrayEquals(ltArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseCyclicReplacementRotationGtArrayLength_thenRotateArrayOk() { + + cyclicReplacement(arr, rotationGtArrayLength); + assertArrayEquals(gtArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseCyclicReplacementRotationEqArrayLength_thenDoNothing() { + int[] clone = arr.clone(); + + cyclicReplacement(arr, arr.length); + assertArrayEquals(clone, arr); + } + + @Test + void givenInputArray_whenUseReverseRotationLtArrayLength_thenRotateArrayOk() { + + reverse(arr, rotationLtArrayLength); + assertArrayEquals(ltArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseReverseRotationGtArrayLength_thenRotateArrayOk() { + + reverse(arr, rotationGtArrayLength); + assertArrayEquals(gtArrayLengthRotation, arr); + } + + @Test + void givenInputArray_whenUseReverseRotationEqArrayLength_thenDoNothing() { + + int[] clone = arr.clone(); + + reverse(arr, arr.length); + assertArrayEquals(clone, arr); + } +}