[leetcode]Combination Sum II @ Python

原题地址：https://oj.leetcode.com/problems/combination-sum-ii/

题意：

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the combination.

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 10,1,2,7,6,1,5 and target 8, 
A solution set is: 
[1, 7] 
[1, 2, 5] 
[2, 6] 
[1, 1, 6] 

解题思路：和上一道题类似。只不过这道题要求candidate中的每个数只能使用一次。也是使用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 and valuelist not in Solution.ret: return Solution.ret.append(valuelist)
        for i in range(start, length):
            if target < candidates[i]:
                return
            self.DFS(candidates, target - candidates[i], i + 1, valuelist + [candidates[i]])
    
    def combinationSum2(self, candidates, target):
        candidates.sort()
        Solution.ret = []
        self.DFS(candidates, target, 0, [])
        return Solution.ret