Generate N-Size Combinations from a List

Create a function that returns all combinations of size n from a list. Sort the list in ascending lexicographical order.

Examples

combo([1, 2, 3, 4], 1) ➞ [[1], [2], [3], [4]]

combo([1, 2, 3, 4], 2) ➞ [[1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4]]

combo([1, 2, 3, 4], 5) ➞ []

combo([1, 2, 3, 4], 0) ➞ [[]]

Notes

• Lexicographical order: Compare the first element: [1, 2] will be before [2, 4]. If both share the same first element, compare the second element: [1, 2] is before [1, 3], etc.
• Return an empty list [] if n exceeds the length of the list.
• Return [[]] if n is 0 (see example #4). (Since there is only one combination of length 0: an empty list).