Using Scheme higher-order function map to implement the string encryption and decryption. 1.1 The encryption function must (1) take the encryption key (key can be between 1 and 4) from the keyboard using (read); and (2) encrypt alphabetic characters and digits only.
1.2 The decryption function must (1) Use the same encryption key from 1.1 for decryption and (2) decrypt the string generated from your encryption function.
Note: When you encrypt a valid character (letters and digits), you add a key to the character. When you decrypt, you will have a different set of the valid characters, which is caused by +key. You can limit the allowed key value to be 1, 2, 3, and 4.