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#2227 - Encrypt and Decrypt Strings

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Array String Hash Table Design Trie

Problem Description

You are given a character array keys containing unique characters and a string array values containing strings of length 2. You are also given another string array dictionary that contains all permitted original strings after decryption. You should implement a data structure that can encrypt or decrypt a 0-indexed string.

A string is encrypted with the following process:

  1. For each character c in the string, we find the index i satisfying keys[i] == c in keys.
  2. Replace c with values[i] in the string.

Note that in case a character of the string is not present in keys, the encryption process cannot be carried out, and an empty string "" is returned.

A string is decrypted with the following process:

  1. For each substring s of length 2 occurring at an even index in the string, we find an i such that values[i] == s. If there are multiple valid i, we choose any one of them. This means a string could have multiple possible strings it can decrypt to.
  2. Replace s with keys[i] in the string.

Implement the Encrypter class:

  • Encrypter(char[] keys, String[] values, String[] dictionary) Initializes the Encrypter class with keys, values, and dictionary.
  • String encrypt(String word1) Encrypts word1 with the encryption process described above and returns the encrypted string.
  • int decrypt(String word2) Returns the number of possible strings word2 could decrypt to that also appear in dictionary.

Solution

/**
 * @param {character[]} keys
 * @param {string[]} values
 * @param {string[]} dictionary
 */
var Encrypter = function(keys, values, dictionary) {
  this.encryptMap = new Map();
  this.validEncryptions = new Map();

  for (let i = 0; i < keys.length; i++) {
    this.encryptMap.set(keys[i], values[i]);
  }

  for (const word of dictionary) {
    const encrypted = this.encrypt(word);
    if (encrypted !== '') {
      this.validEncryptions.set(encrypted, (this.validEncryptions.get(encrypted) || 0) + 1);
    }
  }
};

/**
 * @param {string} word1
 * @return {string}
 */
Encrypter.prototype.encrypt = function(word1) {
  let result = '';

  for (const char of word1) {
    if (!this.encryptMap.has(char)) {
      return '';
    }
    result += this.encryptMap.get(char);
  }

  return result;
};

/**
 * @param {string} word2
 * @return {number}
 */
Encrypter.prototype.decrypt = function(word2) {
  return this.validEncryptions.get(word2) || 0;
};