https://programmers.co.kr/learn/courses/30/lessons/43165
function solution(numbers, target) {
var answer = 0;
function turn(idx, result){
if(idx == numbers.length){
if(target == result){
answer++;
}
return;
}
turn(idx + 1, result + numbers[idx]);
turn(idx + 1, result - numbers[idx]);
}
turn(0, 0);
return answer;
}