377. Combination Sum IV

递归 TLE

class Solution {
public:
    int combinationSum4(vector<int>& nums, int target) {
        if (target == 0)    return 1;
        int res = 0;
        for (int n : nums) {
            if (n <= target) {
                res += combinationSum4(nums, target - n);
            }
        }
        return res;
    }
};

DP

class Solution {
public:
    int combinationSum4(vector<int>& nums, int target) {
        vector<int> dp(target+1, 0);
        dp[0] = 1;
        sort(nums.begin(), nums.end());
        for (int i = 0; i < target; i++) {
            for (int n : nums) {
                if (i+n > target) break;
                dp[i+n] += dp[i];
            }
        }
        return dp[target];
    }
};