How should I practice Encrypt and Decrypt Strings?

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Encrypt and Decrypt Strings

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Problem statement

Build an encrypter from three constructor inputs:

keys[i] is a unique one-character key;
values[i] is the two-character encryption for that key; and
dictionary contains valid plaintext words.

Process each row [method, word] in operations:

encrypt: replace every character of word with its mapped two-character value. If any character has no key, the result is the empty string.
decrypt: count dictionary entries whose complete encryption equals word.

Return one string per operation in order. An encryption result is returned directly; a decryption count is returned in decimal form. Different keys may share the same encrypted value.

Function

processEncrypter(keys: String[], values: String[], dictionary: String[], operations: String[][]) → String[]

Examples

Example 1

keys = ["a","b","c","d"]values = ["ei","zf","ei","am"]dictionary = ["abcd","acbd","adbc","badc","dacb","cadb","cbda","abad"]operations = [["encrypt","abcd"],["decrypt","eizfeiam"]]return = ["eizfeiam","2"]

abcd encrypts to eizfeiam. Exactly abcd and abad in the dictionary produce that ciphertext.

Example 2

keys = ["a","b"]values = ["aa","bb"]dictionary = ["ab","ba"]operations = [["encrypt","ac"],["decrypt","aabb"]]return = ["","1"]

The first word contains an unmapped character. Only ab encrypts to aabb.

Constraints

1 <= keys.length == values.length <= 26.
Every key is a distinct lowercase English character represented as a one-character string.
Every value contains exactly two lowercase English characters; values need not be unique.
1 <= dictionary.length <= 100, and dictionary words contain only lowercase English letters.
1 <= operations.length <= 100.
An encrypt word has length at most 2000.
A decrypt word has positive even length at most 200.