[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 (a₁, a₂, … , a_k) must be in non-descending order. (ie, a₁ â‰¤ a₂ â‰¤ … ≤ a_k).
• 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:    }