Add MinSumKSizeSubarray algorithm (#6025)

Author: rashi07dashore

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

@@ -0,0 +1,51 @@
+package com.thealgorithms.slidingwindow;
+/**
+ * The Sliding Window algorithm is used to find the minimum sum of a subarray
+ * of a fixed size k within a given array.
+ *
+ * <p>
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(1)
+ *
+ * This class provides a static method to find the minimum sum of a subarray
+ * with a specified length k.
+ *
+ * @author Rashi Dashore (https://github.com/rashi07dashore)
+ */
+public final class MinSumKSizeSubarray {
+
+    // Prevent instantiation
+    private MinSumKSizeSubarray() {
+    }
+
+    /**
+     * This method finds the minimum sum of a subarray of a given size k.
+     *
+     * @param arr is the input array where the minimum sum needs to be found
+     * @param k   is the size of the subarray
+     * @return the minimum sum of the subarray of size k
+     */
+    public static int minSumKSizeSubarray(int[] arr, int k) {
+        if (arr.length < k) {
+            return -1; // Edge case: not enough elements
+        }
+
+        int minSum;
+        int windowSum = 0;
+
+        // Calculate the sum of the first window
+        for (int i = 0; i < k; i++) {
+            windowSum += arr[i];
+        }
+        minSum = windowSum;
+
+        // Slide the window across the array
+        for (int i = k; i < arr.length; i++) {
+            windowSum += arr[i] - arr[i - k];
+            minSum = Math.min(minSum, windowSum);
+        }
+        return minSum;
+    }
+}

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

@@ -0,0 +1,79 @@
+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the MinSumKSizeSubarray class.
+ *
+ * @author Rashi Dashore (https://github.com/rashi07dashore)
+ */
+class MinSumKSizeSubarrayTest {
+
+    /**
+     * Test for the basic case of finding the minimum sum.
+     */
+    @Test
+    void testMinSumKSizeSubarray() {
+        int[] arr = {2, 1, 5, 1, 3, 2};
+        int k = 3;
+        int expectedMinSum = 6; // Corrected: Minimum sum of a subarray of size 3
+        assertEquals(expectedMinSum, MinSumKSizeSubarray.minSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for a different array and subarray size.
+     */
+    @Test
+    void testMinSumKSizeSubarrayWithDifferentValues() {
+        int[] arr = {1, 2, 3, 4, 5};
+        int k = 2;
+        int expectedMinSum = 3; // 1 + 2
+        assertEquals(expectedMinSum, MinSumKSizeSubarray.minSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for edge case with insufficient elements.
+     */
+    @Test
+    void testMinSumKSizeSubarrayWithInsufficientElements() {
+        int[] arr = {1, 2};
+        int k = 3; // Not enough elements
+        int expectedMinSum = -1; // Edge case
+        assertEquals(expectedMinSum, MinSumKSizeSubarray.minSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for large array.
+     */
+    @Test
+    void testMinSumKSizeSubarrayWithLargeArray() {
+        int[] arr = {5, 4, 3, 2, 1, 0, -1, -2, -3, -4};
+        int k = 5;
+        int expectedMinSum = -10; // -1 + -2 + -3 + -4 + 0
+        assertEquals(expectedMinSum, MinSumKSizeSubarray.minSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for array with negative numbers.
+     */
+    @Test
+    void testMinSumKSizeSubarrayWithNegativeNumbers() {
+        int[] arr = {-1, -2, -3, -4, -5};
+        int k = 2;
+        int expectedMinSum = -9; // -4 + -5
+        assertEquals(expectedMinSum, MinSumKSizeSubarray.minSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for the case where k equals the array length.
+     */
+    @Test
+    void testMinSumKSizeSubarrayWithKEqualToArrayLength() {
+        int[] arr = {1, 2, 3, 4, 5};
+        int k = 5;
+        int expectedMinSum = 15; // 1 + 2 + 3 + 4 + 5
+        assertEquals(expectedMinSum, MinSumKSizeSubarray.minSumKSizeSubarray(arr, k));
+    }
+}