diff --git a/DIRECTORY.md b/DIRECTORY.md index b7707a254ab6..bad138b341e1 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -207,6 +207,7 @@ * [PriorityQueues](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/PriorityQueues.java) * [Queue](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/Queue.java) * [QueueByTwoStacks](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/QueueByTwoStacks.java) + * [SlidingWindowMaximum](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximum.java) * [TokenBucket](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/TokenBucket.java) * stacks * [NodeStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/NodeStack.java) @@ -882,6 +883,7 @@ * [PriorityQueuesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/PriorityQueuesTest.java) * [QueueByTwoStacksTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java) * [QueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/QueueTest.java) + * [SlidingWindowMaximumTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximumTest.java) * [TokenBucketTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/TokenBucketTest.java) * stacks * [NodeStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java) diff --git a/src/main/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximum.java b/src/main/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximum.java new file mode 100644 index 000000000000..d6720dd01e29 --- /dev/null +++ b/src/main/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximum.java @@ -0,0 +1,63 @@ +package com.thealgorithms.datastructures.queues; + +import java.util.Deque; +import java.util.LinkedList; + +/** + * The {@code SlidingWindowMaximum} class provides a method to efficiently compute + * the maximum element within every sliding window of size {@code k} in a given array. + * + *

The algorithm uses a deque to maintain the indices of useful elements within + * the current sliding window. The time complexity of this approach is O(n) since + * each element is processed at most twice. + * + * @author Hardvan + */ +public final class SlidingWindowMaximum { + private SlidingWindowMaximum() { + } + + /** + * Returns an array of the maximum values for each sliding window of size {@code k}. + *

If {@code nums} has fewer elements than {@code k}, the result will be an empty array. + *

Example: + *

+     * Input: nums = [1, 3, -1, -3, 5, 3, 6, 7], k = 3
+     * Output: [3, 3, 5, 5, 6, 7]
+     * 
+ * + * @param nums the input array of integers + * @param k the size of the sliding window + * @return an array containing the maximum element for each sliding window + */ + public static int[] maxSlidingWindow(int[] nums, int k) { + int n = nums.length; + if (n < k || k == 0) { + return new int[0]; + } + + int[] result = new int[n - k + 1]; + Deque deque = new LinkedList<>(); + for (int i = 0; i < n; i++) { + // Remove elements from the front of the deque if they are out of the current window + if (!deque.isEmpty() && deque.peekFirst() < i - k + 1) { + deque.pollFirst(); + } + + // Remove elements from the back if they are smaller than the current element + while (!deque.isEmpty() && nums[deque.peekLast()] < nums[i]) { + deque.pollLast(); + } + + // Add the current element's index to the deque + deque.offerLast(i); + + // Store the maximum element for the current window (starting from the k-1th element) + if (i >= k - 1) { + result[i - k + 1] = nums[deque.peekFirst()]; + } + } + + return result; + } +} diff --git a/src/test/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximumTest.java b/src/test/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximumTest.java new file mode 100644 index 000000000000..e435f9192a88 --- /dev/null +++ b/src/test/java/com/thealgorithms/datastructures/queues/SlidingWindowMaximumTest.java @@ -0,0 +1,50 @@ +package com.thealgorithms.datastructures.queues; + +import static org.junit.jupiter.api.Assertions.assertArrayEquals; + +import java.util.stream.Stream; +import org.junit.jupiter.params.ParameterizedTest; +import org.junit.jupiter.params.provider.Arguments; +import org.junit.jupiter.params.provider.MethodSource; + +public class SlidingWindowMaximumTest { + + @ParameterizedTest + @MethodSource("provideTestCases") + public void testMaxSlidingWindow(int[] nums, int k, int[] expected) { + assertArrayEquals(expected, SlidingWindowMaximum.maxSlidingWindow(nums, k)); + } + + private static Stream provideTestCases() { + return Stream.of( + // Test case 1: Example from the problem statement + Arguments.of(new int[] {1, 3, -1, -3, 5, 3, 6, 7}, 3, new int[] {3, 3, 5, 5, 6, 7}), + + // Test case 2: All elements are the same + Arguments.of(new int[] {4, 4, 4, 4, 4}, 2, new int[] {4, 4, 4, 4}), + + // Test case 3: Window size equals the array length + Arguments.of(new int[] {2, 1, 5, 3, 6}, 5, new int[] {6}), + + // Test case 4: Single element array with window size 1 + Arguments.of(new int[] {7}, 1, new int[] {7}), + + // Test case 5: Window size larger than the array length + Arguments.of(new int[] {1, 2, 3}, 4, new int[] {}), + + // Test case 6: Decreasing sequence + Arguments.of(new int[] {9, 8, 7, 6, 5, 4}, 3, new int[] {9, 8, 7, 6}), + + // Test case 7: Increasing sequence + Arguments.of(new int[] {1, 2, 3, 4, 5}, 2, new int[] {2, 3, 4, 5}), + + // Test case 8: k is zero + Arguments.of(new int[] {1, 3, -1, -3, 5, 3, 6, 7}, 0, new int[] {}), + + // Test case 9: Array with negative numbers + Arguments.of(new int[] {-4, -2, -5, -1, -3}, 3, new int[] {-2, -1, -1}), + + // Test case 10: Empty array + Arguments.of(new int[] {}, 3, new int[] {})); + } +}