Prevent overflow in sliding average updates

Author: krotname

src/main/java/algorithms/sprint0/SlidingAverage.java

@@ -28,7 +28,7 @@ static List<Double> movingAverage(int n, List<Integer> arr, int windowSize) {
         }
         result.add(sum / (double) windowSize);
         for (int i = windowSize; i < minSize; i++) {
-            sum += arr.get(i) - arr.get(i - windowSize);
+            sum += (long) arr.get(i) - arr.get(i - windowSize);
             result.add(sum / (double) windowSize);
         }
         return result;

src/test/java/algorithms/sprint0/SlidingAverageTest.java

@@ -49,6 +49,13 @@ void largeValuesDoNotOverflowTheWindowSum() {
         assertListDoubles(SlidingAverage.movingAverage(4, List.of(max, max, max, max), 2), max, max, max);
     }
 
+    @Test
+    void extremeValuesDoNotOverflowTheRollingUpdate() {
+        assertListDoubles(SlidingAverage.movingAverage(
+                2, List.of(Integer.MIN_VALUE, Integer.MAX_VALUE), 1),
+                Integer.MIN_VALUE, Integer.MAX_VALUE);
+    }
+
     private static void assertListDoubles(List<Double> actual, double... expected) {
         assertEquals(expected.length, actual.size(), "size");
         for (int i = 0; i < expected.length; i++) {