Combination Sum II

Posted 2020-07-04

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, … , a_k) must be in non-descending order. (ie, a₁ ≤ a₂ ≤ … ≤ a_k).
• 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:
   void dfs(const vector<int>& candidates,int target,vector<vector<int> >& res,vector<int>& dummy,int index){
        if(target<0){
            return;
        }
        else if(target==0){
            for(int i=0;i<res.size();i++)
                if(res[i]==dummy)
                    return;
            res.push_back(dummy);
            return;
        }
        for(int i=index;i<candidates.size();i++){
            dummy.push_back(candidates[i]);
            dfs(candidates,target-candidates[i],res,dummy,i+1);
            dummy.pop_back();//典型的回溯思想
        }
    }
    vector<vector<int> > combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin(),candidates.end());
        vector<vector<int> >res;
        vector<int> dummy;
        dfs(candidates,target,res,dummy,0);
        return res;
    }
};