leetcode—— 39——Combination Sum

Given a set of candidate numbers (C) and a target number (T), find all unique combinations inC 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();                     }     }};