[C#]프로그래머스/타겟 넘버/DFS

public class Solution
{
    private int answer = 0;
 
    public int solution(int[] numbers, int target)
    {
        DFS(0, -1, numbers, target);
        return answer;
    }
 
    private void DFS(int sum, int index, int[] numbers, int target)
    {
        //꼭 배열을 다 순회해야한다.
        if (index + 1 >= numbers.Length)
        {
            if (sum == target)
                answer++;
 
            return;
        }
 
        index++;
 
        DFS(sum + numbers[index], index, numbers, target);
        DFS(sum - numbers[index], index, numbers, target);
    }
}