add string to number

is-palindrome.ts

@@ -0,0 +1,32 @@
+import type { Equal, Expect } from '@type-challenges/utils'
+
+type casesPalindrome = [
+  Expect<Equal<IsPalindrome<'abc'>, false>>,
+  Expect<Equal<IsPalindrome<'b'>, true>>,
+  Expect<Equal<IsPalindrome<'abca'>, false>>,
+  Expect<Equal<IsPalindrome<'abcba'>, true>>,
+  Expect<Equal<IsPalindrome<121>, true>>,
+  Expect<Equal<IsPalindrome<19260817>, false>>,
+]
+
+type CheckPalindrome<
+    T extends string[]
+> = 
+T extends [infer First, ...infer Mid, infer Last]
+    ? First extends Last
+        ? Mid extends string[] ? CheckPalindrome<Mid> : never
+        : false
+    : true
+;
+
+type ToArr<T extends string> = T extends `${infer Head}${infer Tail}` ? [Head, ...ToArr<Tail>] : [];
+
+type IsPalindrome<
+    T extends string | number
+> = 
+T extends number
+    ? IsPalindrome<`${T}`>
+: T extends string
+    ? CheckPalindrome<ToArr<T>>
+: never
+

string-to-number.ts

@@ -0,0 +1,31 @@
+import type { Equal, Expect } from '@type-challenges/utils'
+
+type cases = [
+  Expect<Equal<ToNumber<'0'>, 0>>,
+  Expect<Equal<ToNumber<'5'>, 5>>,
+  Expect<Equal<ToNumber<'12'>, 12>>,
+  Expect<Equal<ToNumber<'27'>, 27>>,
+  Expect<Equal<ToNumber<'18@7_$%'>, never>>,
+]
+
+type Digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';
+
+type IsNumber<
+  S extends string,
+> =
+S extends `${Digit}${infer Tail}`
+  ? IsNumber<Tail>
+  : S extends ''
+    ? true
+    : false
+;
+
+type ToNumber<
+  S extends string,
+  Acc extends 1[] = []
+> =
+IsNumber<S> extends true
+  ? `${Acc['length']}` extends S
+    ? Acc['length']
+    : ToNumber<S, [...Acc, 1]>
+  : never