// Program to calculate the sum of all elements in an array 
//   both iteratively and recursively.
// Demonstrates public-private pair approach to recursion.

public class ArraySum {
   public static void main(String[] args) {
      int[] numbers = {5, 1, 0, -4, 12, 2, -7, 2};
      System.out.println(arraySumIter(numbers));
      System.out.println(arraySumRecur(numbers));
   }
   
   // calculates the sum of the elements in arr
   public static int arraySumIter(int[] arr) {
      int sum = 0;
      for (int i = 0; i < arr.length; i++) {
         sum += arr[i];
      }
      return sum;
   }
   
   // calculates the sum of the elements in arr
   //
   // public version of the method that has the signature 
   //   expected by the client
   public static int arraySumRecur(int[] arr) {
      return arraySumRecur(arr, 0);
   }
   
   // calculates the sum of the elements in arr
   //
   // private version that includes an additional parameter
   //   to track where in the array we are currently working
   private static int arraySumRecur(int[] arr, int index) {
      if (arr.length == index) {
         return 0;
      } else {
         // get current element
         int elem = arr[index];
         // sum up rest of array
         int sum = arraySumRecur(arr, index + 1);
         // return current element plus sum of rest
         return elem + sum;
         
      }
   }
}