fix: reject negative input in SumOfSquares and add tests

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

@@ -5,7 +5,6 @@
  * Find minimum number of perfect squares that sum to given number
  *
  * @see <a href="https://en.wikipedia.org/wiki/Lagrange%27s_four-square_theorem">Lagrange's Four Square Theorem</a>
- * @author BEASTSHRIRAM
  */
 public final class SumOfSquares {
 
@@ -16,10 +15,15 @@ private SumOfSquares() {
     /**
      * Find minimum number of perfect squares that sum to n
      *
-     * @param n the target number
+     * @param n the target number (must be non-negative)
      * @return minimum number of squares needed
+     * @throws IllegalArgumentException if 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

@@ -1,13 +1,12 @@
 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;
 
 /**
  * Test class for SumOfSquares
- *
- * @author BEASTSHRIRAM
  */
 class SumOfSquaresTest {
 
@@ -65,4 +64,11 @@ void testEdgeCases() {
         // Test edge case
         assertEquals(1, SumOfSquares.minSquares(0)); // 0^2
     }
+
+    @Test
+    void testNegativeInput() {
+        // Negative inputs should throw IllegalArgumentException
+        assertThrows(IllegalArgumentException.class, () -> SumOfSquares.minSquares(-1));
+        assertThrows(IllegalArgumentException.class, () -> SumOfSquares.minSquares(-10));
+    }
 }