## Saturday, January 26, 2013

### [LeetCode] Combination Sum, Solution

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, â€¦ , ak) must be in non-descending order. (ie, a1 â‰¤ a2 â‰¤ â€¦ â‰¤ 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]`
» Solve this problem

[Thoughts]
This is a normal recursion question. For each candidate, add and verify the target. If it hit, add it as a part of solution.

[Code]
``````1:    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
2:      // Start typing your C/C++ solution below
3:      // DO NOT write int main() function
4:      vector<vector<int> > result;
5:      vector<int> solution;
6:      int sum=0;
7:      std::sort(candidates.begin(), candidates.end());
8:      GetCombinations(candidates,sum, 0, target, solution, result);
9:      return result;
10:    }
11:    void GetCombinations(
12:      vector<int>& candidates,
13:      int& sum,
14:      int level,
15:      int target,
16:      vector<int>& solution,
17:      vector<vector<int> >& result)
18:    {
19:      if(sum > target) return;
20:      if(sum == target)
21:      {
22:        result.push_back(solution);
23:        return;
24:      }
25:      for(int i =level; i< candidates.size(); i++)
26:      {
27:        sum+=candidates[i];
28:        solution.push_back(candidates[i]);
29:        GetCombinations(candidates, sum, i, target, solution, result);
30:        solution.pop_back();
31:        sum-=candidates[i];
32:      }
33:    }
``````