//騰訊面試。
class Solution {
public:
    int result = 0;
    void dfs(int sum, int cnt, vector<int>&nums, int S)
    {
        if(cnt==nums.size()){
            if(sum==S)
                result+=1;
            return;
        }
        dfs(sum+nums[cnt], cnt+1, nums, S);
        dfs(sum-nums[cnt], cnt+1, nums, S);
    }
    int findTargetSumWays(vector<int>& nums, int S) {
        dfs(0, 0, nums, s);
        return result;
    }
};