BitwiseXOR

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题目

Implement BitwiseXOR<S1,S2> which takes two binary string literal type and returns a binary string that reprents the bitwise XOR of S1 and S2

For example:

BitwiseXOR<"0", "1">; // expect '1'
BitwiseXOR<"1", "1">; // expect '0'
BitwiseXOR<"10", "1">; // expect '11'

解答

type MakePrefix<
  S extends string,
  P extends string = ""
> = S extends `${string}${infer R}` ? MakePrefix<R, `${P}0`> : P;

type Pad<S1 extends string, S2 extends string> = [S1, S2] extends [
  `${string}${infer RS1}`,
  `${string}${infer RS2}`
]
  ? Pad<RS1, RS2>
  : [MakePrefix<S2>, MakePrefix<S1>];

type _XOR<S1 extends string, S2 extends string, R extends string = ""> = [
  S1,
  S2
] extends [`${infer F1}${infer R1}`, `${infer F2}${infer R2}`]
  ? _XOR<R1, R2, `${R}${F1 extends F2 ? "0" : "1"}`>
  : R;

type BitwiseXOR<S1 extends string, S2 extends string> = Pad<S1, S2> extends [
  infer P1 extends string,
  infer P2 extends string
]
  ? _XOR<`${P1}${S1}`, `${P2}${S2}`>
  : never;