class Solution:
    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
        def backtrack(start, target, path):
            if target == 0:
                result.append(path[:])
                return
            for i in range(start, len(candidates)):
                if candidates[i] > target:
                    break
                path.append(candidates[i])
                backtrack(i, target - candidates[i], path)
                path.pop()
        
        result = []
        candidates.sort()
        backtrack(0, target, [])
        return result

class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(candidates);
        backtrack(result, new ArrayList<>(), candidates, target, 0);
        return result;
    }

    private void backtrack(List<List<Integer>> result, List<Integer> tempList, int[] candidates, int remain, int start) {
        if (remain < 0) return;
        else if (remain == 0) result.add(new ArrayList<>(tempList));
        else {
            for (int i = start; i < candidates.length; i++) {
                tempList.add(candidates[i]);
                backtrack(result, tempList, candidates, remain - candidates[i], i);  // not i + 1 because we can reuse same elements
                tempList.remove(tempList.size() - 1);
            }
        }
    }

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<vector<int>> result;
        sort(candidates.begin(), candidates.end());
        vector<int> current;
        backtrack(candidates, target, 0, current, result);
        return result;
    }

private:
    void backtrack(const vector<int>& candidates, int target, int start, vector<int>& current, vector<vector<int>>& result) {
        if (target == 0) {
            result.push_back(current);
            return;
        }
        for (int i = start; i < candidates.size() && candidates[i] <= target; i++) {
            current.push_back(candidates[i]);
            backtrack(candidates, target - candidates[i], i, current, result);
            current.pop_back();
        }
    }