프로그래머스 Lv2 타켓 넘버

https://programmers.co.kr/learn/courses/30/lessons/43165

function solution(numbers, target) {
  var answer=0;
    function dfs(count,val){
        if(count==numbers.length){
          if(target == val){
            answer+=1;
          }
        }else{
          dfs(count+1,val+numbers[count])
          dfs(count+1,val-numbers[count]);
        }
    };
    dfs(0,0);
    return answer;
}