BAEL-6913 - Rotate array in java (#14861)
* feat: rotate array in java * fix: When to when
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lucaCambi77
GitHub
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package com.baeldung.algorithms.rotatearray;
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/**
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* 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.
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* Therefore, a large rotation number will be translated into the relative smallest rotation.
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* All solutions replace the original array, although they might use an extra array to compute the rotation.
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*/
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public class RotateArray {
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private RotateArray() {
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throw new IllegalStateException("Rotate array algorithm utility methods class");
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}
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/**
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*
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* @param arr array to apply rotation to
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* @param k number of rotations
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*/
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public static void bruteForce(int[] arr, int k) {
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checkInvalidInput(arr, k);
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k %= arr.length;
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int temp;
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int previous;
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for (int i = 0; i < k; i++) {
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previous = arr[arr.length - 1];
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for (int j = 0; j < arr.length; j++) {
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temp = arr[j];
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arr[j] = previous;
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previous = temp;
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}
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}
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}
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/**
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*
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* @param arr array to apply rotation to
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* @param k number of rotations
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*/
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public static void withExtraArray(int[] arr, int k) {
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checkInvalidInput(arr, k);
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int[] extraArray = new int[arr.length];
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for (int i = 0; i < arr.length; i++) {
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extraArray[(i + k) % arr.length] = arr[i];
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}
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System.arraycopy(extraArray, 0, arr, 0, arr.length);
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}
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/**
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*
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* @param arr array to apply rotation to
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* @param k number of rotations
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*/
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public static void cyclicReplacement(int[] arr, int k) {
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checkInvalidInput(arr, k);
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k = k % arr.length;
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int count = 0;
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for (int start = 0; count < arr.length; start++) {
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int current = start;
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int prev = arr[start];
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do {
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int next = (current + k) % arr.length;
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int temp = arr[next];
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arr[next] = prev;
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prev = temp;
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current = next;
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count++;
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} while (start != current);
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}
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}
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/**
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*
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* @param arr array to apply rotation to
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* @param k number of rotations
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*/
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public static void reverse(int[] arr, int k) {
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checkInvalidInput(arr, k);
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k %= arr.length;
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reverse(arr, 0, arr.length - 1);
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reverse(arr, 0, k - 1);
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reverse(arr, k, arr.length - 1);
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}
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private static void reverse(int[] nums, int start, int end) {
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while (start < end) {
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int temp = nums[start];
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nums[start] = nums[end];
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nums[end] = temp;
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start++;
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end--;
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}
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}
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private static void checkInvalidInput(int[] arr, int rotation) {
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if (rotation < 1 || arr == null)
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throw new IllegalArgumentException("Rotation must be greater than zero or array must be not null");
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}
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}
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package com.baeldung.algorithms.rotatearray;
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import static com.baeldung.algorithms.rotatearray.RotateArray.bruteForce;
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import static com.baeldung.algorithms.rotatearray.RotateArray.cyclicReplacement;
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import static com.baeldung.algorithms.rotatearray.RotateArray.reverse;
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import static com.baeldung.algorithms.rotatearray.RotateArray.withExtraArray;
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import static org.junit.jupiter.api.Assertions.assertArrayEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import org.junit.jupiter.api.Test;
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class RotateArrayUnitTest {
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private final int[] arr = { 1, 2, 3, 4, 5, 6 };
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private final int rotationLtArrayLength = 1;
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private final int rotationGtArrayLength = arr.length + 2;
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private final int[] ltArrayLengthRotation = { 6, 1, 2, 3, 4, 5 };
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private final int[] gtArrayLengthRotation = { 5, 6, 1, 2, 3, 4 };
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@Test
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void givenInputArray_whenNoRotationOrEmptyArray_thenThrowIllegalArgumentException() {
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final int noRotation = 0;
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final int someRotation = arr.length - 1;
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assertThrows(IllegalArgumentException.class, () -> bruteForce(arr, noRotation));
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assertThrows(IllegalArgumentException.class, () -> withExtraArray(arr, noRotation));
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assertThrows(IllegalArgumentException.class, () -> cyclicReplacement(arr, noRotation));
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assertThrows(IllegalArgumentException.class, () -> reverse(arr, noRotation));
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assertThrows(IllegalArgumentException.class, () -> bruteForce(null, someRotation));
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assertThrows(IllegalArgumentException.class, () -> withExtraArray(null, someRotation));
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assertThrows(IllegalArgumentException.class, () -> cyclicReplacement(null, someRotation));
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assertThrows(IllegalArgumentException.class, () -> reverse(null, someRotation));
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}
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@Test
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void givenInputArray_whenUseBruteForceRotationLtArrayLength_thenRotateArrayOk() {
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bruteForce(arr, rotationLtArrayLength);
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assertArrayEquals(ltArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseBruteForceRotationGtArrayLength_thenRotateArrayOk() {
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bruteForce(arr, rotationGtArrayLength);
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assertArrayEquals(gtArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseBruteForceRotationEqArrayLength_thenDoNothing() {
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int[] expected = arr.clone();
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bruteForce(arr, arr.length);
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assertArrayEquals(expected, arr);
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}
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@Test
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void givenInputArray_whenUseExtraArrayRotationLtArrayLength_thenRotateArrayOk() {
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withExtraArray(arr, rotationLtArrayLength);
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assertArrayEquals(ltArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseExtraArrayRotationGtArrayLength_thenRotateArrayOk() {
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withExtraArray(arr, rotationGtArrayLength);
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assertArrayEquals(gtArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseExtraArrayWithRotationEqArrayLength_thenDoNothing() {
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int[] clone = arr.clone();
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withExtraArray(arr, arr.length);
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assertArrayEquals(clone, arr);
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}
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@Test
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void givenInputArray_whenUseCyclicReplacementRotationLtArrayLength_thenRotateArrayOk() {
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cyclicReplacement(arr, rotationLtArrayLength);
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assertArrayEquals(ltArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseCyclicReplacementRotationGtArrayLength_thenRotateArrayOk() {
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cyclicReplacement(arr, rotationGtArrayLength);
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assertArrayEquals(gtArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseCyclicReplacementRotationEqArrayLength_thenDoNothing() {
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int[] clone = arr.clone();
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cyclicReplacement(arr, arr.length);
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assertArrayEquals(clone, arr);
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}
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@Test
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void givenInputArray_whenUseReverseRotationLtArrayLength_thenRotateArrayOk() {
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reverse(arr, rotationLtArrayLength);
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assertArrayEquals(ltArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseReverseRotationGtArrayLength_thenRotateArrayOk() {
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reverse(arr, rotationGtArrayLength);
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assertArrayEquals(gtArrayLengthRotation, arr);
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}
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@Test
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void givenInputArray_whenUseReverseRotationEqArrayLength_thenDoNothing() {
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int[] clone = arr.clone();
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reverse(arr, arr.length);
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assertArrayEquals(clone, arr);
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}
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}
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