LeetCode:Combinations

LeetCode: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],
]

class Solution {
public:
    vector > combine(int n, int k) {
        vector> res;
        if(n<1||k<1||n temp;
        collect(n,k,0,temp,res);
        return res;
    }
        void collect(int n,int k,int i,vector &temp,vector> &res)
        {
            if(temp.size()==k)
            {
                res.push_back(temp);
                return;
            }
            for(;i