39. Combination Sum 组合之和

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of times.

Note:

All numbers (including target) will be positive integers. The solution set must not contain duplicate combinations.

Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
,
[2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
[2,2,2,2],
[2,3,3],
[3,5]
]

Difficulty: Mediaum

class Solution {
public:
vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
vector<vector<int>> res;
vector<int> solution;
findSum(candidates, 0, target, solution, res);
return res;
}

void findSum(vector<int>& candidates,int start,int target,vector<int>& solution,vector<vector<int>>& res){
if (target<0) return;
else if (target==0) res.push_back(solution);
else {
for (int i = start; i < candidates.size(); i++) {
solution.push_back(candidates[i]);
findSum(candidates, i, target-candidates[i], solution, res);
solution.pop_back();
}
}
}
};