快開學了...我還能撐到30天嗎><
使用dp就不要想著一步登天，要從頭就紀錄方法數到尾(ps:dp到現在還是不大會用......)

ref:https://leetcode.com/problems/combination-sum-iv/solutions/4020273/easy-c-recursive-iterative-dp-beats-100-with-debug-info/?envType=daily-question&envId=2023-09-09

class Solution {
public:
    int combinationSum4(vector<int>& nums, int target) {
        vector<unsigned> dp(target + 1, 0);
        dp[0] = 1;
        for(int i = 1; i <= target; i++){
            for(int x : nums){
                if(i >= x){
                    dp[i] += dp[i - x];
                }
            }
        }
        return dp[target];
    }
};