40. Combination Sum II (Recursion)

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) {
        results.clear();
        vector<int> result;
        sort(candidates.begin(), candidates.end());
        dfs(candidates, result,target, 0);
        return results;
    }

    void dfs(vector<int> &candidates, vector<int> &result, int target, int depth)
    {
        if(candidates[depth] > target || depth == candidates.size()) return;
        result.push_back(candidates[depth]);
        if(candidates[depth] == target)
        {
            results.push_back(result);
            result.pop_back();
            return;
        }
        dfs(candidates,result, target-candidates[depth], depth+1);
        result.pop_back();
        while(++depth<candidates.size()  && candidates[depth] == candidates[depth-1]); //avoid repetition
        dfs(candidates,result, target, depth);
    }
private:
    vector<vector<int> > results;
};