Combination Sum IV (Leetcode 377)

这里上传两种解法：

1. Memorized Search:

    unordered_map<int, int> mp;
    int combinationSum4(vector<int>& nums, int target) {
        if(nums.empty() || target < 0) return 0;
        if(target == 0) return 1;
        else if(mp.count(target)){
            return mp[target];
        }
        int res = 0;
        for(int i=0; i<nums.size(); i++){
            res += combinationSum4(nums, target - nums[i]);
        }
        mp[target] = res;
        return res;
    }
};

2.DP:

   vector<int> dp(target+1, 0);
   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];