LeetCode-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, … , 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] 

Solution:

Code:

<span style="font-size:14px;">class Solution {public:    void helper(const vector<int> &candidates, int target, const int &length, int index, vector<vector<int> > &results, vector<int> &result) {        if (target == 0) {            results.push_back(result);            return;        }        if (target < 0) return;        for (int i = index; i < length; ++i) {            result.push_back(candidates[i]);            helper(candidates, target-candidates[i], length, i, results, result);            result.pop_back();            if (target-candidates[i] < 0) break;        }    }        vector<vector<int> > combinationSum(vector<int> &candidates, int target) {        const int length = candidates.size();        sort(candidates.begin(), candidates.end());        vector<vector<int> > results;        vector<int> result;        helper(candidates, target, length, 0, results, result);        return results;    }};</span>