Utility Types — Record<K, V>

Record<K, V> creates an object type with keys of type K and values of type V.

Implement two functions:

1. `groupBy<T>(items: T[], key: keyof T): Record<string, T[]>`
Groups items by the value of key.

2. `invertRecord(rec: Record<string, string>): Record<string, string>`
Swaps keys and values.

Examples

• groupBy([{lang:'js'},{lang:'ts'},{lang:'js'}], 'lang') → { js: [{lang:'js'},{lang:'js'}], ts: [{lang:'ts'}] }
• invertRecord({ a: '1', b: '2' }) → { '1': 'a', '2': 'b' }