25270-transpose.ts

/**
 * 25270 - Transpose
 *
 * The transpose of a matrix is an operator which flips a matrix over its diagonal; that is,
 * it switches the row and column indices of the matrix A by producing another matrix, often denoted by A<sup>T</sup>.
 *
 * ```ts
 * type Matrix = Transpose <[[1]]>; // expected to be [[1]]
 * type Matrix1 = Transpose <[[1, 2], [3, 4]]>; // expected to be [[1, 3], [2, 4]]
 * type Matrix2 = Transpose <[[1, 2, 3], [4, 5, 6]]>; // expected to be [[1, 4], [2, 5], [3, 6]]
 * ```
 */

/* _____________ Your Code Here _____________ */

type Transpose<M extends number[][], O extends unknown[][] = []> = M extends [infer A, ...infer Rest extends number[][]]
  ? O extends []
    ? { [K in keyof A]: [A[K]] } extends infer Arr extends unknown[][]
      ? Transpose<Rest, Arr>
      : never
    : { [K in keyof O]: K extends keyof A ? [...O[K], A[K]] : O[K] } extends infer Arr extends unknown[][]
      ? Transpose<Rest, Arr>
      : never
  : O

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Transpose<[]>, []>>,
  Expect<Equal<Transpose<[[1]]>, [[1]]>>,
  Expect<Equal<Transpose<[[1, 2]]>, [[1], [2]]>>,
  Expect<Equal<Transpose<[[1, 2], [3, 4]]>, [[1, 3], [2, 4]]>>,
  Expect<Equal<Transpose<[[1, 2, 3], [4, 5, 6]]>, [[1, 4], [2, 5], [3, 6]]>>,
  Expect<Equal<Transpose<[[1, 4], [2, 5], [3, 6]]>, [[1, 2, 3], [4, 5, 6]]>>,
  Expect<Equal<Transpose<[[1, 2, 3], [4, 5, 6], [7, 8, 9]]>, [[1, 4, 7], [2, 5, 8], [3, 6, 9]]>>,
]