LeetCode in Python 39. Combination Sum

https://leetcode.com/problems/combination-sum/

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]
]

 Solution:

class Solution(object):
    def combinationSum(self, candidates, target):
        """
        :type candidates: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        res = []
        candidates.sort()
        
        def dfs(start, out, target):       
            if not target:
                res.append(out)
                return

            for i in range(start, len(candidates)):
                if candidates[i] > target: break
                dfs(i, out+[candidates[i]], target-candidates[i])

        dfs(0, [], target)
        return res

经典dfs题，这个题的dfs思路是先从小到大排序，再从小的开始search。比如candidates=[1,2,3]，target=5，dfs的路径是这样的：1->1->1->1->1, 1->1->1->2, 1->1->3……