39. Combination Sum（dfs）

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

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

Note:

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

Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
[7],
[2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
[2,2,2,2],
[2,3,3],
[3,5]
]

class Solution:
    def combinationSum(self, candidates, target):
        """
        :type candidates: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        res = []
        candidates.sort()
        def dfs(i,target,s):
            if i>=len(candidates):
                return
            if candidates[i]==target:
                res.append(s+[candidates[i]])
                return
            if target<=0:
                return
            dfs(i+1,target,s)
            dfs(i,target-candidates[i],s+[candidates[i]])
        dfs(0,target,[])
        return res