Combination Sum 全排列求和

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

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]​​

class Solution {
public:

    void solve( vector<int> candidates,int index,int sum,int target, vector< vector<int> > &res, vector<int> &path)
    {
        if(sum>target)
            return ;
        if(sum==target)
        {
            res.push_back(path);
            return ;
        }
        for(int i=index;i<candidates.size();i++)
        {
            sum+=candidates[i];
            path.push_back(candidates[i]);
            solve(candidates,i,sum,target,res,path);
            path.pop_back();
            sum-=candidates[i];
        }
    }
    
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        //回溯法
        sort(candidates.begin(),candidates.end());  
        vector< vector<int> > res;
        vector <int> path;
        solve(candidates,0,0,target,res,path);
        return res;
    }
    
    
};