40. Combination Sum II

题目描述：

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.
• The solution set must not contain duplicate combinations.

题目要求给出一个正整数数组，与一个目标整数，求出所有和为目标数的所有组合。每一个数只能出现一次。先对数组进行排序，按深度优先遍历，如果结果符合则存到结果向量中。代码如下:

class Solution {public:    vector<vector<int> > combinationSum2(vector<int> &num, int target) {        sort(num.begin(), num.end());        vector<vector<int> > ret;        vector<int> cur;        Helper(ret, cur, num, target, 0);        return ret;    }    void Helper(vector<vector<int> > &ret, vector<int> cur, vector<int> &num, int target, int position)    {        if(target == 0)            ret.push_back(cur);        else        {            for(int i = position; i < num.size() && num[i] <= target; i ++)            {                if(i != position && num[i] == num[i-1])                    continue;                cur.push_back(num[i]);                Helper(ret, cur, num, target-num[i], i+1);                cur.pop_back();            }        }    }};