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Problem Description
Given two integers A and B, return all possible combinations of B numbers out of 1 2 3 ... A.

Make sure the combinations are sorted.

To elaborate,

Within every entry, elements should be sorted. [1, 4] is a valid entry while [4, 1] is not.
Entries should be sorted within themselves.
WARNING: DO NOT USE LIBRARY FUNCTION FOR GENERATING COMBINATIONS.



Problem Constraints
1 <= A, B <= 10



Input Format
The first argument is an integer A.
The second argument is an integer B.



Output Format
Return a 2-D vector denoting all possible combinations.



Example Input
Input 1:

 A = 4
 B = 2
Input 2:

 A = 3
 B = 2


Example Output
Output 1:

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

 [
  [1, 2],
  [1, 3],
  [2, 3]
 ] 


Example Explanation
Explanation 1:

All the possible combinations of size 2 in sorted order.