[!Typescript] 82. Medium – Combination

Given an array of strings, do Permutation & Combination. It’s also useful for the prop types like video controlsList

// expected to be `"foo" | "bar" | "baz" | "foo bar" | "foo bar baz" | "foo baz" | "foo baz bar" | "bar foo" | "bar foo baz" | "bar baz" | "bar baz foo" | "baz foo" | "baz foo bar" | "baz bar" | "baz bar foo"`
type Keys = Combination<['foo', 'bar', 'baz']>

type Combination<T extends string[], U = T[number], K = U> = K extends U
  ? K extends string
    ? K | `${K} ${Combination<[], Exclude<U, K>>}`
    : ''
  : '';

原文地址：http://www.cnblogs.com/Answer1215/p/16844227.html