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>