原题地址：https://oj.leetcode.com/problems/combination-sum/
题意：
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.
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]
解题思路：穷举出符合条件的组合，我们一般考虑dfs。
代码：
class Solution: # @param candidates, a list of integers # @param target, integer # @return a list of lists of integers def DFS(self, candidates, target, start, valuelist): length = len(candidates) if target == 0: return Solution.ret.append(valuelist) for i in range(start, length): if target < candidates[i]: return self.DFS(candidates, target - candidates[i], i, valuelist + [candidates[i]]) def combinationSum(self, candidates, target): candidates.sort() Solution.ret = [] self.DFS(candidates, target, 0, []) return Solution.ret