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]

class Solution {
public:
void internalCombinationSum(vector<int> &candidates,
int start,
int sum,
int target,
vector<int> &combination,
vector<vector<int> > &result) {
int size = candidates.size();

if (sum == target) {
result.push_back(combination);

return;
}
else if ((start >= size) || (sum > target)) {
return;
}

for (int i = start; i < size; ) {
int v = candidates[i];

combination.push_back(v);
internalCombinationSum(candidates, i, sum + v, target, combination, result);
combination.pop_back();

int j = i + 1;

while (j < size) {
if (candidates[i] == candidates[j]) {
++j;
}
else {
break;
}
}

i = j;
}
}

vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
vector<vector<int> > result;
vector<int> combination;

sort(candidates.begin(), candidates.end());
internalCombinationSum(candidates, 0, 0, target, combination, result);

return result;
}
};