둘만의 암호

export function ourSecret(s: string, skip: string, index: number) {
  const alphabet = [...'abcdefghijklmnopqrstuvwxyz'].filter((char) => !skip.includes(char));
  const skipIndex = (char: string) => {
    return alphabet[(alphabet.indexOf(char) + index) % alphabet.length];
  };
 
  return [...s].map(skipIndex).join('');
}