IsPalindrome

题目来源(type-challenges)

问题 #

type case1 = IsPalindrome<'abc'> // false
type case2 = IsPalindrome<'b'> // true
type case3 = IsPalindrome<'abca'> // false
type case4 = IsPalindrome<121> // true
type case5 = IsPalindrome<19260817> // false

解答 #

type Count<T extends string> = T extends `${infer Head}${infer Tail}` ? [Head, ...Count<Tail>] : []
type IsPalindrome1<T extends string | number> = 
Count<`${T}`>['length'] extends 1
? true
: `${T}` extends `${infer Head}${infer C}${infer Tail}`
  ? Head extends Tail
    ? IsPalindrome<C>
    : false
  : false

type Reverse<T extends string> = T extends `${infer Head}${infer Tail}` ? `${Reverse<Tail>}${Head}` : T;

type IsPalindrome<T extends string | number> = `${T}` extends Reverse<`${T}`> ? true : false

拆分 #

1. 数字拆分

• 拿出头尾字符进行比较
• 如果相等就拿剩下的字符递归比较
• 直到剩余长度为 1 返回结果

2. 倒转对比

• 把字符字符串反转
• 对比反转后的字符串