Leetcode：Combination Sum II

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> &num, int target) {        // Note: The Solution object is instantiated only once and is reused by each test case.        vector<vector<int> > v_results;        if(num.empty() )            return v_results;           sort(num.begin(),num.end() );        vector<int> result;        helper(num,0,target,result,v_results);        return v_results;    }    void helper(vector<int>& candidates,int pos,int target,vector<int>& result,vector<vector<int> >& v_results)    {           if(target==0)        {               v_results.push_back(result);            return;        }           if(target<0 || pos>=candidates.size() )            return;        //qu        result.push_back(candidates[pos]);        helper(candidates,pos+1,target-candidates[pos],result,v_results);        result.pop_back();        //not qu        int tmp=pos;        while(tmp<candidates.size()-1 && candidates[tmp]==candidates[tmp+1])            tmp++;        helper(candidates,tmp+1,target,result,v_results);    }   };

需要注意去重，这是个多重背包问题。可以统计每个数字出现的个数，此题就转化成了Combination Sum