Combinations

Description

Given two integers n and k, return all possible combinations of k numbers out of 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 <= 20
• 1 <= k <= n

Solution(javascript)

const combine = function (n, k) {
  const result = []
  const aux = (index = 1, current = []) => {
    if (current.length === k) {
      result.push(current)
      return
    }
    if (index > n) {
      return
    }
    aux(index + 1, [...current, index])
    aux(index + 1, current)
  }
  aux()
  return result
}