fix: reject negative input in SumOfSquares

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

@@ -18,8 +18,13 @@ private SumOfSquares() {
      *
      * @param n the target number
      * @return minimum number of squares needed
+     * @throws IllegalArgumentException if {@code n} is negative
      */
     public static int minSquares(int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("Input must be non-negative");
+        }
+
         if (isPerfectSquare(n)) {
             return 1;
         }

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

@@ -1,6 +1,7 @@
 package com.thealgorithms.maths;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
@@ -65,4 +66,9 @@ void testEdgeCases() {
         // Test edge case
         assertEquals(1, SumOfSquares.minSquares(0)); // 0^2
     }
+
+    @Test
+    void testNegativeInput() {
+        assertThrows(IllegalArgumentException.class, () -> SumOfSquares.minSquares(-1));
+    }
 }