Combinations

Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].

You may return the answer in any order.

Examples

Example 1:

Input: n = 4, k = 2

Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]

Explanation: There are C(4,2) = 6 ways to choose 2 numbers from [1,2,3,4]. Note that combinations are unordered, so [1,2] and [2,1] are considered the same.

Example 2:

Input: n = 1, k = 1

Output: [[1]]

Explanation: There is only one combination: [1].

Constraints

• 1 <= n <= 20
• 1 <= k <= n