[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

[leetcode]Combination Sum @ Python,布布扣,bubuko.com