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Permutation

介绍​

实现联合类型的全排列，将联合类型转换成所有可能的全排列数组的联合类型。 例如

ts
    type perm = Permutation<'A' | 'B' | 'C'>; 
    // ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']
ts
    type perm = Permutation<'A' | 'B' | 'C'>; 
    // ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type Permutation<T> = any
 
/* _____________ Test Cases _____________ */
 
 
 
type cases = [
  Expect<Equal<Permutation<'A'>, ['A']>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<'A' | 'B' | 'C'>, ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<'B' | 'A' | 'C'>, ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<boolean>, [false, true] | [true, false]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<never>, []>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
ts
/* _____________ Your Code Here _____________ */
 
type Permutation<T> = any
 
/* _____________ Test Cases _____________ */
 
 
 
type cases = [
  Expect<Equal<Permutation<'A'>, ['A']>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<'A' | 'B' | 'C'>, ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<'B' | 'A' | 'C'>, ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<boolean>, [false, true] | [true, false]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Permutation<never>, []>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
]
 
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解决方案​

Spoiler warning // Click to reveal answer
ts
/**
 * 这是按顺序做题以来遇到的, 用法都认识, 但就是想不出来解决方案,却又寄希望未知的某个特性一下解决的的那类问题.
 * 最佳答案解释的很详细, 也有中文翻译.
 * 但中文版中提供了解决这类问题的最核心一点: 算法
 * ：[Generating Permutations - Topcoder](https://www.topcoder.com/blog/generating-permutations) 
 * 本文的思路就是第一种: remove
 *  BASIC ALGORITHM 1: REMOVE（基础算法之 删除 算法）
    BASIC ALGORITHM 2: INSERT（基础算法之 插入 算法）
    BASIC ALGORITHM 3: LEXICOGRAPHIC（基础算法之 字典序 算法）
    HEAP’S ALGORITHM（高级算法之 堆 算法）
 */
 
type Exclude2<T, U> = T extends U ? never : T;
 
type Permutation<All, K = All> = [All] extends [never]
  ? []
  : K extends All
    ? [K, ...Permutation<Exclude2<All, K>>]
    : never
 
ts
/**
 * 这是按顺序做题以来遇到的, 用法都认识, 但就是想不出来解决方案,却又寄希望未知的某个特性一下解决的的那类问题.
 * 最佳答案解释的很详细, 也有中文翻译.
 * 但中文版中提供了解决这类问题的最核心一点: 算法
 * ：[Generating Permutations - Topcoder](https://www.topcoder.com/blog/generating-permutations) 
 * 本文的思路就是第一种: remove
 *  BASIC ALGORITHM 1: REMOVE（基础算法之 删除 算法）
    BASIC ALGORITHM 2: INSERT（基础算法之 插入 算法）
    BASIC ALGORITHM 3: LEXICOGRAPHIC（基础算法之 字典序 算法）
    HEAP’S ALGORITHM（高级算法之 堆 算法）
 */
 
type Exclude2<T, U> = T extends U ? never : T;
 
type Permutation<All, K = All> = [All] extends [never]
  ? []
  : K extends All
    ? [K, ...Permutation<Exclude2<All, K>>]
    : never
 
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