LeetCode Combination Sum

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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] 

 1 // 17:10

 2 class Solution {

 3 private:

 4     vector<vector<int> > res;

 5 public:

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

 7         res.clear();

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

 9         vector<int> path;

10         dfs(candidates, candidates.size() - 1, target, path);

11         return res;

12     }

13     

14     void dfs(vector<int>& candidates, int pos, int target, vector<int>& path) {

15         if (target == 0) {

16             res.push_back(path);

17             reverse(res.back().begin(), res.back().end());

18             return;

19         }

20         if (target < 0 || pos < 0) {

21             return;

22         }

23         

24         int curv = candidates[pos];

25         

26         // don't use current value

27         dfs(candidates, pos - 1, target, path);

28         int cnt = 0;

29         while (target > 0) {

30             path.push_back(curv);

31             target -= curv;

32             dfs(candidates, pos - 1, target, path);

33             cnt++;

34         }

35         

36         path.resize(path.size() - cnt);

37     }

38 };