Given an array of unique elements, return all possible subsequences.
A subsequence is a sequence that can be derived from an array by deleting some or no elements without changing the order of the remaining elements.
For example:
type A = Subsequence<[1, 2]> // [] | [1] | [2] | [1, 2]
import type { Equal, Expect } from '@type-challenges/utils'
type cases = [
Expect<Equal<Subsequence<[1, 2]>, [] | [1] | [2] | [1, 2]>>,
Expect<Equal<Subsequence<[1, 2, 3]>, [] | [1] | [2] | [1, 2] | [3] | [1, 3] | [2, 3] | [1, 2, 3]>>,
Expect<Equal<Subsequence<[1, 2, 3, 4, 5]>, [] |
[1] | [2] | [3] | [4] | [5] |
[1, 2] | [1, 3] | [1, 4] | [1, 5] | [2, 3] | [2, 4] | [2, 5] | [3, 4] | [3, 5] | [4, 5] |
[1, 2, 3] | [1, 2, 4] | [1, 2, 5] | [1, 3, 4] | [1, 3, 5] | [1, 4, 5] | [2, 3, 4] | [2, 3, 5] | [2, 4, 5] | [3, 4, 5] |
[1, 2, 3, 4] | [1, 2, 3, 5] | [1, 2, 4, 5] | [1, 3, 4, 5] | [2, 3, 4, 5] |
[1, 2, 3, 4, 5] >>,
Expect<Equal<Subsequence<['a', 'b', 'c']>, [] |
['a'] | ['b'] | ['c'] |
['a', 'b'] | ['a', 'c'] | ['b', 'c'] |
['a', 'b', 'c'] >>,
Expect<Equal<Subsequence<['x', 'y']>, [] |
['x'] | ['y'] |
['x', 'y'] >>,
]