Add Longest Subarray With Sum Less Than or Equal to K algorithm and tests

Author: Chiefpatwal

src/main/java/com/thealgorithms/slidingwindow/LongestSubarrayWithSumLessOrEqualToK.java

@@ -0,0 +1,48 @@
+package com.thealgorithms.slidingwindow;
+
+/**
+ * The Longest Subarray with Sum Less Than or Equal to k algorithm finds the length
+ * of the longest subarray whose sum is less than or equal to a given value k.
+ *
+ * <p>
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(1)
+ *
+ * @author https://github.com/Chiefpatwal
+ */
+public final class LongestSubarrayWithSumLessOrEqualToK {
+
+    // Prevent instantiation
+    private LongestSubarrayWithSumLessOrEqualToK() {
+    }
+
+    /**
+     * This method finds the length of the longest subarray with a sum less than or equal to k.
+     *
+     * @param arr is the input array
+     * @param k   is the maximum sum allowed
+     * @return the length of the longest subarray with sum less than or equal to k
+     */
+    public static int longestSubarrayWithSumLEK(int[] arr, int k) {
+        int maxLength = 0; // To store the maximum length found
+        int currentSum = 0; // To store the current sum of the window
+        int left = 0; // Left index of the sliding window
+
+        for (int right = 0; right < arr.length; right++) {
+            currentSum += arr[right]; // Expand the window to the right
+
+            // Shrink the window from the left if the current sum exceeds k
+            while (currentSum > k && left <= right) {
+                currentSum -= arr[left]; // Remove the leftmost element
+                left++; // Move the left index to the right
+            }
+
+            // Update maxLength if the current window is valid
+            maxLength = Math.max(maxLength, right - left + 1);
+        }
+
+        return maxLength; // Return the maximum length found
+    }
+}

src/test/java/com/thealgorithms/slidingwindow/LongestSubarrayWithSumLessOrEqualToKTest.java

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+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the LongestSubarrayWithSumLessOrEqualToK algorithm.
+ */
+public class LongestSubarrayWithSumLessOrEqualToKTest {
+
+    /**
+     * Tests for the longest subarray with a sum less than or equal to k.
+     */
+    @Test
+    public void testLongestSubarrayWithSumLEK() {
+        assertEquals(3, LongestSubarrayWithSumLessOrEqualToK.longestSubarrayWithSumLEK(new int[] {1, 2, 3, 4}, 6)); // {1, 2, 3}
+        assertEquals(4, LongestSubarrayWithSumLessOrEqualToK.longestSubarrayWithSumLEK(new int[] {1, 2, 3, 4}, 10)); // {1, 2, 3, 4}
+        assertEquals(2, LongestSubarrayWithSumLessOrEqualToK.longestSubarrayWithSumLEK(new int[] {5, 1, 2, 3}, 5)); // {5}
+        assertEquals(0, LongestSubarrayWithSumLessOrEqualToK.longestSubarrayWithSumLEK(new int[] {1, 2, 3}, 0)); // No valid subarray
+    }
+}