这题是我蠢了，它说是组合数我就信了，言尽于此

class Solution {
public:
    int combinationSum4(vector<int>& nums, int target) {
        vector<int> dp(2000,0);
        dp[0]=1;
        for(int i=0;i<=target;i++){
            for(int j=0;j<nums.size();j++){
                if(i>=nums[j]&& dp[i] < INT_MAX - dp[i - nums[j]])
                    dp[i]+=dp[i-nums[j]];
            }
        }
        return dp[target];
    }
};