leetcode—— 39——Combination Sum

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

class Solution {
public: 
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) 
    { 
        vector<vector<int>> result;
        vector<int> path; 
        sort(candidates.begin(),candidates.end());
        helper(candidates,0,target,path,result); 
        return result;
        
        
    } 
    void helper(vector<int> &nums,int pos,int target,vector<int>& path,vector<vector<int>> & result) 
    { 
        if(0==target)
        {
            result.push_back(path); 
            return ; 
            
        } 
        if(target < 0) return ;
        for(int i=pos;i<nums.size();i++) 
        { 
            path.push_back(nums[i]);
            helper(nums,i,target-nums[i],path,result);
            path.pop_back(); 
            
        }
     }
};