Code

class Solution {
public:
    vector<vector<int>> result;
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        std::sort(candidates.begin(), candidates.end());
        vector<int> cur;
        dfs(cur, candidates, 0, 0, target);
        std::sort(result.begin(), result.end());
        result.erase(std::unique(result.begin(), result.end()), result.end());
        return result;
    }

    void dfs(vector<int> cur, vector<int> candidates, int base, int value, int target) {
        for (int i=base; i<candidates.size(); i++) {
            if (value + candidates[i] < target) {
                cur.push_back(candidates[i]);
                dfs(cur, candidates, i, value+candidates[i], target);
                cur.pop_back();
                continue;
            }
            else if (value + candidates[i] == target) {
                cur.push_back(candidates[i]);
                result.push_back(cur);
            }
            return;
        }
    }
};