const int N = 1010;

class Solution {
public:

    unsigned dp[N];  //注意dp的中间值可能会爆内存，所以把int改为unsigned

    int combinationSum4(vector<int>& nums, int target) {
        int n = nums.size();

        dp[0] = 1;
        for(int i = 1; i <= target; i++){
            for(int j = 0; j < n; j++){
                if(i >= nums[j]){
                    dp[i] += dp[i - nums[j]];
                }
            }
        }
        return dp[target];
    }
};