[leetcode][回溯] Combination Sum II

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] 

class Solution {public:    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {        vector<vector<int> > res;        if(candidates.empty()) return res;        sort(candidates.begin(), candidates.end());        vector<int> oneCombination;        combinationSum2Core(candidates, 0, target, oneCombination, res);        return res;    }private:    void combinationSum2Core(vector<int>& candidates, int start, int target, vector<int> oneCombination,  vector<vector<int> > &res){        for(int i = start; i < candidates.size(); ++i){            if(i != start && candidates[i] == candidates[i-1]) continue;//去重            if(candidates[i] > target) return;            oneCombination.push_back(candidates[i]);            if(candidates[i] == target) {                res.push_back(oneCombination);                return;            }            combinationSum2Core(candidates, i+1, target-candidates[i], oneCombination, res);//如果取了当前值，就要前进            oneCombination.pop_back();        }    }};