feat(slidingwindow): add SmallestSubarrayWithSum algorithm

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

@@ -0,0 +1,18 @@
+package com.thealgorithms.slidingwindow;
+
+public class SmallestSubarrayWithSum {
+
+    public static int smallestSubarrayLen(int[] arr, int target) {
+        if (arr == null || arr.length == 0) return 0;
+        int left = 0, sum = 0, minLen = Integer.MAX_VALUE;
+
+        for (int right = 0; right < arr.length; right++) {
+            sum += arr[right];
+            while (sum >= target) {
+                minLen = Math.min(minLen, right - left + 1);
+                sum -= arr[left++];
+            }
+        }
+        return minLen == Integer.MAX_VALUE ? 0 : minLen;
+    }
+}

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

@@ -0,0 +1,50 @@
+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for SmallestSubarrayWithSum algorithm
+ */
+public class SmallestSubarrayWithSumTest {
+
+    @Test
+    public void testBasicCase() {
+        int[] arr = {2, 3, 1, 2, 4, 3};
+        int target = 7;
+        int expected = 2; // subarray [4,3]
+        assertEquals(expected, SmallestSubarrayWithSum.smallestSubarrayLen(arr, target));
+    }
+
+    @Test
+    public void testNoValidSubarray() {
+        int[] arr = {1, 1, 1, 1};
+        int target = 10;
+        int expected = 0; // no subarray reaches target
+        assertEquals(expected, SmallestSubarrayWithSum.smallestSubarrayLen(arr, target));
+    }
+
+    @Test
+    public void testSingleElement() {
+        int[] arr = {5};
+        int target = 5;
+        int expected = 1;
+        assertEquals(expected, SmallestSubarrayWithSum.smallestSubarrayLen(arr, target));
+    }
+
+    @Test
+    public void testAllElementsSame() {
+        int[] arr = {2, 2, 2, 2, 2};
+        int target = 6;
+        int expected = 3;
+        assertEquals(expected, SmallestSubarrayWithSum.smallestSubarrayLen(arr, target));
+    }
+
+    @Test
+    public void testLargeInput() {
+        int[] arr = {1, 2, 3, 4, 5, 6};
+        int target = 11;
+        int expected = 2; // subarray [5,6]
+        assertEquals(expected, SmallestSubarrayWithSum.smallestSubarrayLen(arr, target));
+    }
+}