LeetCode Combination Sum

这题居然没有记录，写一下吧：

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

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 2,3,6,7 and target 7, 
A solution set is: 
[7] 
[2, 2, 3] 

// 17:10
class Solution {
private:
    vector<vector<int> > res;
public:
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        res.clear();
        sort(candidates.begin(), candidates.end());
        vector<int> path;
        dfs(candidates, candidates.size() - 1, target, path);
        return res;
    }
    
    void dfs(vector<int>& candidates, int pos, int target, vector<int>& path) {
        if (target == 0) {
            res.push_back(path);
            reverse(res.back().begin(), res.back().end());
            return;
        }
        if (target < 0 || pos < 0) {
            return;
        }
        
        int curv = candidates[pos];
        
        // don't use current value
        dfs(candidates, pos - 1, target, path);
        int cnt = 0;
        while (target > 0) {
            path.push_back(curv);
            target -= curv;
            dfs(candidates, pos - 1, target, path);
            cnt++;
        }
        
        path.resize(path.size() - cnt);
    }
};