Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,
If n = 4 and k = 2, a solution is:

[

  [2,4],

  [3,4],

  [2,3],

  [1,2],

  [1,3],

  [1,4],

]

分析：组合的实现，之前实现过全排列，递归求解

class Solution {

public:

    vector<vector<int>> combine(int n, int k) {

        //爆搜

        vector<vector<int>> res;

        if (k== || n==)

            return res;

        for(int base=; base<=(n-k+); base++){

            vector<int> tempres(,base);

            helper(base,n,k-,tempres,res);

        }

        return res;

    }

    void helper(int base,int n, int num, vector<int>& tempres, vector<vector<int>>& res){

        if(num==){

            res.push_back(tempres);

            return;

        }

        if(base+num->n){

            return;

        }

        for(int i=base+; i<=n; i++){

            tempres.push_back(i);

            helper(i,n,num-,tempres,res);

            tempres.pop_back();

        }

    }

};

巴特西

Combinations

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