打卡题目：leetcode第39题，组合总和
    相似题目：40
    image.png

    【代码】

    1. class Solution:
    2.     def __init__(self):
    3.         self.res = []
    4.         self.candidates = []
    5.     def get_candidates(self, candidates):
    6.         candidates.sort()
    7.         self.candidates = candidates
    8.     def get_res(self, sums, target, now, loc):
    9.         if sums + self.candidates[0] > target:
    10.             return False
    11.         for i in range(len(self.candidates)):
    12.             if i < loc:
    13.                 continue
    14.             num = self.candidates[i]
    15.             if num + sums == target:
    16.                 self.res.append(now+[num])
    17.             elif num + sums > target:
    18.                 return False
    19.             else:
    20.                 self.get_res(sums+num, target, now+[num], i)
    21.     def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
    22.         self.get_candidates(candidates)
    23.         self.get_res(0, target, [], 0)
    24.         return self.res