39. Combination Sum

재귀 호출 돌리면서 target 값이 되면 result에 저장하면 되는 문제 

    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
        results = []

        def dfs(index, cur, path):
            if cur < 0:
                return
            if cur == 0:
                results.append(path)
                return

            for i in range(index, len(candidates)):
                dfs(i, cur-candidates[i], path + [candidates[i]])

        dfs(0, target, [])
        return results