[leetcode]Combination Sum @ Python

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