class Main {

    public static int findTargetSumWays(int[] nums, int s) {

        return backtrack(nums, 0, 0, s);

    }

​

    private static int backtrack(int[] nums, int index, int sum, int s) {

        if (index == nums.length) {

            return sum == s ? 1 : 0;

        }

        return backtrack(nums, index + 1, sum + nums[index], s)

            + backtrack(nums, index + 1, sum - nums[index], s);

    }

    public static void main(String[] args) {

        int[] nums = {

            8,

            7,

            1,

            5,

            3,

            8,

            11,

            6,

            14

        };

        System.out.println(findTargetSumWays(nums, 15));

    }

}