【leetcode】Combination Sum

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 (a₁, a₂, … , a_k) must be in non-descending order. (ie, a₁ ≤ a₂ ≤ … ≤ 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] 

利用递归搜索，同时剪枝就可以

 

class Solution {

public:

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

        

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

        vector<vector<int> > result;

        vector<int> tmp;

 

        backtracking(result,candidates,target,tmp,0,0);

        

        return result;

    }

    

    void backtracking(vector<vector<int> > &result,vector<int> &candidates, int &target,vector<int> tmp, int sum,int index)

    {

 

        if(sum==target)

        {

            result.push_back(tmp);

            return;

        }

        else

        {

            int sum0=sum;

            //注意index

            for(int i=index;i<candidates.size();i++)

            {

                tmp.push_back(candidates[i]);

                sum=sum0+candidates[i];

                if(sum>target)

                {

                    break;

                }

                backtracking(result,candidates,target,tmp,sum,i);

                tmp.pop_back();

            }            

        }        

    }

};