class Solution:
    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
        N = len(candidates)
        res = []
        def helper(combo, idx, remainder):
            if remainder <= 0:
                if remainder == 0:
                    res.append(combo)
                return
            for i in range(idx, N):
                helper(combo + (candidates[i], ), i, remainder - candidates[i])
        
        helper((), 0, target)
        return res