链接： 组合总和

class Solution:
    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
        res = []
        self.dfs(candidates, target, [], res, 0)
        return res
    
    def dfs(self, candidates, target, path, ans, begin):
        if target == 0:
            ans.append(path)
            return
        
        for i in range(begin, len(candidates)):
            num = candidates[i]
            if num <= target:
                self.dfs(candidates, target-num, path+[num], ans, i+1)