/**
 * Recursive subset sum - an example of using a helper method in recursion.
 */
public class SubsetSum {

    // the "main" subset sum method - just a wrapper around the helper
    public static boolean subsetSum(int[] a, int target) {
        return recSubset(a, target, 0, 0);
    }
    
    // the helper method that does the actual work.
    // includes extra parameters for the values that recursion needs to track.
    private static boolean recSubset(int[] a, int target, int nextIndex, int sumSoFar) {
        if (sumSoFar == target) {
            return true;
        } else if (sumSoFar > target) {
            return false;
        } else if (nextIndex == a.length) {
            return false;
        } else {
            boolean with = recSubset(a, target, nextIndex + 1, sumSoFar + a[nextIndex]);
            boolean without = recSubset(a, target, nextIndex + 1, sumSoFar);
            return with || without;
        }
    }

    public static void main(String[] args) {
        int[] vals = {3, 2, 7, 3, 10};
        System.out.println("13 possible? " + subsetSum(vals, 13));
        System.out.println("14 possible? " + subsetSum(vals, 14));
    }   

}