19.ts

import { Expect, Equal } from "type-testing";

type Tokens = ["🛹", "🚲", "🛴", "🏄", "🛹", "🚲", "🛴"];

type Repeat<Token, Times, Acc extends any[] = []> = Acc["length"] extends Times
  ? Acc
  : Repeat<Token, Times, [...Acc, Token]>;

type Rebuild<List, Acc extends any[] = []> = List extends [
  infer First,
  ...infer Rest,
]
  ? [...Repeat<Tokens[Acc["length"]], First>, ...Rebuild<Rest, [...Acc, First]>]
  : [];

type test_0_actual = Rebuild<[2, 1, 3, 3, 1, 1, 2]>;
//   ^?
type test_0_expected = [
  "🛹",
  "🛹",
  "🚲",
  "🛴",
  "🛴",
  "🛴",
  "🏄",
  "🏄",
  "🏄",
  "🛹",
  "🚲",
  "🛴",
  "🛴",
];
type test_0 = Expect<Equal<test_0_expected, test_0_actual>>;

type test_1_actual = Rebuild<[3, 3, 2, 1, 2, 1, 2]>;
//   ^?
type test_1_expected = [
  "🛹",
  "🛹",
  "🛹",
  "🚲",
  "🚲",
  "🚲",
  "🛴",
  "🛴",
  "🏄",
  "🛹",
  "🛹",
  "🚲",
  "🛴",
  "🛴",
];
type test_1 = Expect<Equal<test_1_expected, test_1_actual>>;

type test_2_actual = Rebuild<[2, 3, 3, 5, 1, 1, 2]>;
//   ^?
type test_2_expected = [
  "🛹",
  "🛹",
  "🚲",
  "🚲",
  "🚲",
  "🛴",
  "🛴",
  "🛴",
  "🏄",
  "🏄",
  "🏄",
  "🏄",
  "🏄",
  "🛹",
  "🚲",
  "🛴",
  "🛴",
];
type test_2 = Expect<Equal<test_2_expected, test_2_actual>>;