# 77. Combinations
Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.
Example:
Input: n = 4, k = 2
Output:
[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]
# Solution
Approach 1: DFS.
# Code (Python)
Approach 1:
# Code (C++)
Approach 1:
class Solution {
private:
void combine(vector<int>& oneCom, vector<vector<int>>& comSet, int head, int tail, int k) {
if (k == 0)
{
comSet.push_back(oneCom);
return;
}
for (int i = head; i <= tail; ++i)
{
oneCom.push_back(i);
combine(oneCom, comSet, i + 1, tail, k - 1);
oneCom.pop_back();
}
}
public:
vector<vector<int>> combine(int n, int k) {
vector<vector<int>> comSet;
vector<int> oneCom;
combine(oneCom, comSet, 1, n, k);
return comSet;
}
};