Recursive Sum of the First n Elements of an Array in Java

We assume that input is a non-zero length integer array.

Base case (Termination condition) : if n == 0 then return 0

General case : return the sum of the first n-1 integers in the array plus the value at the specified index in the array

For the input array {1, 3, 5, 4, 7} find the sum of the first 4 items in the array recursively.

Result is the sum of the items =  1+3+5+4=13

public class SumOfNIntegers {

 
 public static int recursiveArraySum(int[] data, int n)
 {
  if( n==0 )
   return 0;
  else
   return recursiveArraySum(data, n-1) + data[n-1];
 }
 
 public static void main(String[] args) {
  
  int[] inputArray = {1, 3, 5, 4, 7};
  
  int result = recursiveArraySum(inputArray, 3);
  
  System.out.println(result);
  
  result = recursiveArraySum(inputArray, 4);
  
  System.out.println(result);
  
 } 
}

recursiveArraySum method takes input array and the number of items to sum from the beginning of the array.

Console output is :

9

13


Diagram for the recursive method calls :

Reference :  http://www.amazon.com/Data-Structures-Algorithms-Java-Edition-ebook/dp/B00JDRQF8C