fix(maths): detect long overflow in Pow.pow

src/main/java/com/thealgorithms/maths/Pow.java

@@ -16,20 +16,23 @@ private Pow() {
      * <p>
      * The method calculates {@code a}<sup>{@code b}</sup> by iteratively multiplying the base {@code a} with itself {@code b} times.
      * If the exponent {@code b} is negative, an {@code IllegalArgumentException} is thrown.
+     * If the exact result does not fit in a {@code long}, an {@code ArithmeticException} is thrown
+     * instead of silently returning a wrapped-around value.
      * </p>
      *
-     * @param a the base of the exponentiation. Must be a non-negative integer.
+     * @param a the base of the exponentiation.
      * @param b the exponent to which the base {@code a} is raised. Must be a non-negative integer.
      * @return the result of {@code a}<sup>{@code b}</sup> as a {@code long}.
      * @throws IllegalArgumentException if {@code b} is negative.
+     * @throws ArithmeticException if the result overflows a {@code long}.
      */
     public static long pow(int a, int b) {
         if (b < 0) {
             throw new IllegalArgumentException("Exponent must be non-negative.");
         }
         long result = 1;
         for (int i = 1; i <= b; i++) {
-            result *= a;
+            result = Math.multiplyExact(result, a);
         }
         return result;
     }

src/test/java/com/thealgorithms/maths/PowTest.java

@@ -33,4 +33,16 @@ void testPowHandlesZeroBase() {
     void testPowHandlesOneBase() {
         assertEquals(1, Pow.pow(1, 100));
     }
+
+    @ParameterizedTest
+    @CsvSource({"2, 62, 4611686018427387904", "-2, 63, -9223372036854775808", "-3, 3, -27", "-2, 4, 16", "10, 18, 1000000000000000000"})
+    void testPowAtAndNearLongBounds(int base, int exponent, long expected) {
+        assertEquals(expected, Pow.pow(base, exponent));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"2, 63", "2, 64", "-2, 64", "10, 19", "2147483647, 3"})
+    void testPowThrowsOnOverflow(int base, int exponent) {
+        assertThrows(ArithmeticException.class, () -> Pow.pow(base, exponent));
+    }
 }