style: handle empty input array in FindMin.findMin (#4205)

* tests: add test case with mininum not being at the beginning

* style: throw IllegalArgumentException when input is empty

* style: use enhanced for loop

* docs: update doc-str

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

@@ -24,16 +24,20 @@ public class FindMin {
     }
 
     /**
-     * Find the minimum number of an array of numbers.
+     * @brief finds the minimum value stored in the input array
      *
-     * @param array the array contains element
-     * @return min value
+     * @param array the input array
+     * @exception IllegalArgumentException input array is empty
+     * @return the mimum value stored in the input array
      */
     public static int findMin(int[] array) {
-        int min = array[0];
-        for (int i = 1; i < array.length; ++i) {
-            if (array[i] < min) {
-                min = array[i];
+        if (array.length == 0) {
+            throw new IllegalArgumentException("array must be non-empty.");
+        }
+        int min = Integer.MAX_VALUE;
+        for (final var value : array) {
+            if (value < min) {
+                min = value;
             }
         }
         return min;

src/test/java/com/thealgorithms/maths/FindMinTest.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;
 
@@ -23,4 +24,17 @@ public class FindMinTest {
     public void test2() {
         assertEquals(0, FindMin.findMin(new int[] { 0, 192, 384, 576 }));
     }
+
+    @Test
+    public void test3() {
+        assertEquals(0, FindMin.findMin(new int[] { 10, 10, 0, 10 }));
+    }
+
+    @Test
+    public void testFindMinThrowsExceptionForEmptyInput() {
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> FindMin.findMin(new int[]{})
+        );
+    }
 }