Add Maximum Sliding Window algorithm (#5848)

src/main/java/com/thealgorithms/others/MaximumSlidingWindow.java

@@ -0,0 +1,56 @@
+package com.thealgorithms.others;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * Maximum Sliding Window Algorithm
+ *
+ * This algorithm finds the maximum element in each sliding window of size k
+ * in a given array of integers. It uses a deque (double-ended queue) to
+ * efficiently keep track of potential maximum values in the current window.
+ *
+ * Time Complexity: O(n), where n is the number of elements in the input array
+ * Space Complexity: O(k), where k is the size of the sliding window
+ */
+
+public class MaximumSlidingWindow {
+
+    /**
+     * Finds the maximum values in each sliding window of size k.
+     *
+     * @param nums The input array of integers
+     * @param windowSize The size of the sliding window
+     * @return An array of integers representing the maximums in each window
+     */
+    public int[] maxSlidingWindow(int[] nums, int windowSize) {
+        if (nums == null || nums.length == 0 || windowSize <= 0 || windowSize > nums.length) {
+            return new int[0]; // Handle edge cases
+        }
+
+        int[] result = new int[nums.length - windowSize + 1];
+        Deque<Integer> deque = new ArrayDeque<>();
+
+        for (int currentIndex = 0; currentIndex < nums.length; currentIndex++) {
+
+            // Remove the first element if it's outside the current window
+            if (!deque.isEmpty() && deque.peekFirst() == currentIndex - windowSize) {
+                deque.pollFirst();
+            }
+
+            // Remove all elements smaller than the current element from the end
+            while (!deque.isEmpty() && nums[deque.peekLast()] < nums[currentIndex]) {
+                deque.pollLast();
+            }
+
+            // Add the current element's index to the deque
+            deque.offerLast(currentIndex);
+
+            // If we have processed at least k elements, add to result
+            if (currentIndex >= windowSize - 1) {
+                result[currentIndex - windowSize + 1] = nums[deque.peekFirst()];
+            }
+        }
+        return result;
+    }
+}

src/test/java/com/thealgorithms/others/MaximumSlidingWindowTest.java

@@ -0,0 +1,63 @@
+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class MaximumSlidingWindowTest {
+
+    MaximumSlidingWindow msw;
+    int[] nums;
+    int k;
+
+    @BeforeEach
+    void setUp() {
+        msw = new MaximumSlidingWindow(); // Initialize the MaximumSlidingWindow object
+    }
+
+    // Test for a simple sliding window case
+    @Test
+    void testMaxSlidingWindowSimpleCase() {
+        nums = new int[] {1, 3, -1, -3, 5, 3, 6, 7};
+        k = 3;
+        int[] expected = {3, 3, 5, 5, 6, 7};
+        assertArrayEquals(expected, msw.maxSlidingWindow(nums, k));
+    }
+
+    // Test when window size is 1 (output should be the array itself)
+    @Test
+    void testMaxSlidingWindowWindowSizeOne() {
+        nums = new int[] {4, 2, 12, 11, -5};
+        k = 1;
+        int[] expected = {4, 2, 12, 11, -5};
+        assertArrayEquals(expected, msw.maxSlidingWindow(nums, k));
+    }
+
+    // Test when the window size is equal to the array length (output should be a single max element)
+    @Test
+    void testMaxSlidingWindowWindowSizeEqualsArrayLength() {
+        nums = new int[] {4, 2, 12, 11, -5};
+        k = nums.length;
+        int[] expected = {12}; // Maximum of the entire array
+        assertArrayEquals(expected, msw.maxSlidingWindow(nums, k));
+    }
+
+    // Test when the input array is empty
+    @Test
+    void testMaxSlidingWindowEmptyArray() {
+        nums = new int[] {};
+        k = 3;
+        int[] expected = {};
+        assertArrayEquals(expected, msw.maxSlidingWindow(nums, k));
+    }
+
+    // Test when the window size is larger than the array (should return empty)
+    @Test
+    void testMaxSlidingWindowWindowSizeLargerThanArray() {
+        nums = new int[] {1, 2, 3};
+        k = 5;
+        int[] expected = {}; // Window size is too large, so no result
+        assertArrayEquals(expected, msw.maxSlidingWindow(nums, k));
+    }
+}