leetcode 40. Combination Sum II

1.题目

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] 

2.思路 

与上一题不同的是数组中的一个数只可以出现一次。

class Solution {
public:
    void comb(vector<int> candidates, int index, int target, vector<vector<int>> &res, vector<int> &path)
    {
    	if(0>target)return;
		if(0==target){res.push_back(path);return;}
		for(int i= index; i<candidates.size();i++)
		{
			path.push_back(candidates[i]);
			comb(candidates,i+1,target-candidates[i],res,path);
			path.pop_back();
			while(i<candidates.size()-1 && candidates[i]==candidates[i+1])i++; // 防止出现重复的答案
		}
	}
	vector<vector<int> > combinationSum2(vector<int> &candidates, int target) {
        sort(candidates.begin(),candidates.end());
		vector<vector<int>> res;
		vector<int> path;
		comb(candidates,0,target,res,path);
		return res;
    }
};