def __init__(self, groups=None):
        super(GroupedRequirements, self).__init__(NamedRequirements)
        self.groups = groups or self.default_groups
        self.filename = None
        self.create_default_groups()
def combinationSum(self, candidates, target):
        candidates.sort()
        self.result = []
        self.dfs(candidates,target,0,[])
        return self.result