[LeetCode]题解（python）：039-Combination Sum

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题目来源

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

Given a set of candidate numbers (C) 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.

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题意分析

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Input: a list as candidates, a value named target

Output:the list number that sumed to target

Conditions:在list里面找若干个数，使得和为target，注意每个数可以取若干次

Note:

• All numbers (including target) will be positive integers.
• Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• 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]

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题目思路

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先对list进行排序，然后穷举即可

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AC代码（Python）

 _author_ = "YE"
 # -*- coding:utf-8 -*-

 class Solution(object):
     def find(self,candidates, target, start, valueList):
         if target == 0:
             Solution.ans.append(valueList)
         length = len(candidates)
         for i in range(start, length):
             if candidates[i] > target:
                 return
             self.find(candidates, target - candidates[i], i, valueList + [candidates[i]])

     def combinationSum(self, candidates, target):
         """
         :type candidates: List[int]
         :type target: int
         :rtype: List[List[int]]
         """
         candidates.sort()
         Solution.ans = []
         self.find(candidates, target, 0, [])
         return Solution.ans

 s = Solution()
 candidates = [2,3,6,7]
 target = 7
 print(s.combinationSum(candidates, target))