Add HW01 exercises

HW01/Factorial_02.java

@@ -0,0 +1,13 @@
+import java.util.Scanner;
+public class Factorial{
+    public static void main(String[] args){
+        Scanner num = new Scanner(System.in);
+        long n = num.nextInt();
+        long result = 1;
+
+        for (int i=1 ; i <= n; i++){
+            result *= i;
+        }
+        System.out.println(n + "! = " + result);
+    }
+}