vector<vector<int>> combinationSum(vector<int>& candidates, int target) {

std::vector<int> curr;

std::vector<std::vector<int>> res;

helper(candidates, target, 0, curr, res);

return res;

}

void helper(std::vector<int>& cands, int target, int i, std::vector<int>& curr, std::vector<std::vector<int>>& res) {

if (i >= cands.size() || target < 0)

return;

if (target == 0) {

res.push_back(curr);

return;

}

curr.push_back(cands[i]);

helper(cands, target - cands[i], i, curr, res);

curr.pop_back();

helper(cands, target, i + 1, curr, res);

}