type-challenges#19458 - SnakeCase (type-challenges#19459)

Co-authored-by: Gabriel Vergnaud <9265418+gvergnaud@users.noreply.github.com>

questions/19458-hard-snakecase/README.md

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+Create a `SnakeCase<T>` generic that turns a string formatted in **camelCase** into a string formatted in **snake_case**.
+
+A few examples:
+
+```ts
+type res1 = SnakeCase<"hello">; // => "hello"
+type res2 = SnakeCase<"userName">; // => "user_name"
+type res3 = SnakeCase<"getElementById">; // => "get_element_by_id"
+```

questions/19458-hard-snakecase/info.yml

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+difficulty: hard
+title: SnakeCase
+tags: template-literal,string
+author:
+  github: gvergnaud
+  name: Gabriel Vergnaud
+

questions/19458-hard-snakecase/template.ts

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+type SnakeCase<T> = any

questions/19458-hard-snakecase/test-cases.ts

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+import type { Equal, Expect } from '@type-challenges/utils'
+import { ExpectFalse, NotEqual } from '@type-challenges/utils'
+
+type cases = [
+  Expect<Equal<SnakeCase<"hello">, "hello">>,
+  Expect<Equal<SnakeCase<"userName">, "user_name">>,
+  Expect<Equal<SnakeCase<"getElementById">, "get_element_by_id">>,
+  Expect<Equal<SnakeCase<"getElementById" | "getElementByClassNames">, "get_element_by_id" | "get_element_by_class_names">>,
+]