2227. Encrypt and Decrypt Strings

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.

 

Example 1:

Input
["Encrypter", "encrypt", "decrypt"]
[[['a', 'b', 'c', 'd'], ["ei", "zf", "ei", "am"], ["abcd", "acbd", "adbc", "badc", "dacb", "cadb", "cbda", "abad"]], ["abcd"], ["eizfeiam"]]
Output
[null, "eizfeiam", 2]

Explanation
Encrypter encrypter = new Encrypter([['a', 'b', 'c', 'd'], ["ei", "zf", "ei", "am"], ["abcd", "acbd", "adbc", "badc", "dacb", "cadb", "cbda", "abad"]);
encrypter.encrypt("abcd"); // return "eizfeiam". 
                           // 'a' maps to "ei", 'b' maps to "zf", 'c' maps to "ei", and 'd' maps to "am".
encrypter.decrypt("eizfeiam"); // return 2. 
                              // "ei" can map to 'a' or 'c', "zf" maps to 'b', and "am" maps to 'd'. 
                              // Thus, the possible strings after decryption are "abad", "cbad", "abcd", and "cbcd". 
                              // 2 of those strings, "abad" and "abcd", appear in dictionary, so the answer is 2.

 

Constraints:

• 1 <= keys.length == values.length <= 26
• values[i].length == 2
• 1 <= dictionary.length <= 100
• 1 <= dictionary[i].length <= 100
• All keys[i] and dictionary[i] are unique.
• 1 <= word1.length <= 2000
• 2 <= word2.length <= 200
• All word1[i] appear in keys.
• word2.length is even.
• keys, values[i], dictionary[i], word1, and word2 only contain lowercase English letters.
• At most 200 calls will be made to encrypt and decrypt in total.

 

Solutions

Solution: Hash Map

• Time complexity: O(n+mL)
• Space complexity: O(n+mL)

 

JavaScript

/**
 * @param {character[]} keys
 * @param {string[]} values
 * @param {string[]} dictionary
 */
const Encrypter = function (keys, values, dictionary) {
  const n = keys.length;

  this.encryptMap = new Map();
  this.dictionaryMap = new Map();

  for (let index = 0; index < n; index++) {
    const key = keys[index];

    this.encryptMap.set(key, values[index]);
  }

  for (const word of dictionary) {
    const encrypt = this.encrypt(word);
    const count = this.dictionaryMap.get(encrypt) ?? 0;

    this.dictionaryMap.set(encrypt, count + 1);
  }
};

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

  for (const char of word1) {
    result += this.encryptMap.get(char);
  }

  return result;
};

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

/**
 * Your Encrypter object will be instantiated and called as such:
 * var obj = new Encrypter(keys, values, dictionary)
 * var param_1 = obj.encrypt(word1)
 * var param_2 = obj.decrypt(word2)
 */