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],
]
#define vi vector<int>
#define vvi vector<vi >
#define pb push_back
class Solution {
public:
vector<vector<int> > combine(int n, int k) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
......
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