[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 (a1a2, … , 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] 

 

DFS!

 1 class Solution {

 2 public:

 3     void findNext(vector<vector<int> > &res, vector<int> &candidates, vector<int> v, int sum, int target, int idx) {

 4         if (sum > target || idx >= candidates.size()) {

 5             return;

 6         }

 7         if (sum == target) {

 8             res.push_back(v);

 9             return;

10         }

11         v.push_back(candidates[idx]);

12         findNext(res, candidates, v, sum + candidates[idx], target, idx);

13         v.pop_back();

14         findNext(res, candidates, v, sum, target, idx + 1);

15     }

16     

17     vector<vector<int> > combinationSum(vector<int> &candidates, int target) {

18         vector<vector<int> > res;

19         sort(candidates.begin(), candidates.end());

20         vector<int> v;

21         findNext(res, candidates, v, 0, target, 0);

22         return res;

23     }

24 };

 

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