[leetcode]39. Combination Sum

Given a set of candidate numbers (C) (without duplicates) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

 

For example, given candidate set [2, 3, 6, 7] and target 7, 
A solution set is: 

[
  [7],
  [2, 2, 3]
]

 

求所有和为target的可能组合，每个数可以出现多次

思路：DFS，每加入一个值，继续向下遍历别的值，符合条件，加入结果

class Solution(object):
    def combinationSum(self, candidates, target):
        if not candidates or not target:
            return []
        res,ress = [],[]
        self.dfs(sorted(candidates),target,res,ress)
        return ress
    
    def dfs(self,nums,target,res,ress):
        if target < 0: return
        if target==0:
            ress.append(res)
        else:
            for i,v in enumerate(nums):
                if v <= target:
                    self.dfs(nums[i:],target-v,res+[v],ress)
        return