77. Combinations
Medium
Given two integers n and k, return all possible combinations of k numbers out of the range [1, n].
You may return the answer in any order.
Example 1:
Input: n = 4, k = 2
Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]
Example 2:
Input: n = 1, k = 1
Output: [[1]]
Constraints:
1 <= n <= 201 <= k <= n