Encrypt and Decrypt Strings

class Encrypter(object):
    def __init__(self, keys, values, dictionary):
        # Creating the encryption mapping using keys and values
        self.enc = {}
        for k, v in zip(keys, values):
            self.enc[k] = v

        # Counting the frequency of encrypted words in the dictionary
        encrypted_words_counter = collections.Counter()
        for word in dictionary:
            encrypted_word = self.encrypt(word)
            encrypted_words_counter[encrypted_word] += 1

        # Storing the decryption method as a function
        self.decrypt = encrypted_words_counter.__getitem__

    def encrypt(self, word1):
        # Encrypting the given word using the self.enc mapping
        encrypted_word_parts = []
        for c in word1:
            encrypted_char = self.enc.get(c, '#')

        return ''.join(encrypted_word_parts)

Identifying Problem Isomorphism

“Encrypt and Decrypt Strings” can be mapped to “Encode and Decode TinyURL”.

Both are about creating an encoding and decoding scheme. In “Encrypt and Decrypt Strings”, the task is to devise a method to encrypt and decrypt strings. Similarly, in “Encode and Decode TinyURL”, the task is to create a method to encode a long URL into a short alias and then decode the alias back to the original URL.

The problem of encoding and decoding strings is typically more straightforward because it deals with a predefined set of characters and has clear rules. “Encode and Decode TinyURL” is more complex as it includes additional considerations such as handling a larger character set (URL valid characters) and ensuring the uniqueness of the encoded URLs.

10 Prerequisite LeetCode Problems

“2227. Encrypt and Decrypt Strings” involves string manipulation, encryption/decryption algorithms, and bitwise operations. Here are some problems to improve your skills in these areas:

  1. “344. Reverse String”: A basic problem to practice manipulating strings.

  2. “709. To Lower Case”: This problem can help you understand ASCII values of characters, which is often useful in encryption/decryption problems.

  3. “125. Valid Palindrome”: This problem involves string parsing and character comparison, which can be useful for encryption problems.

  4. “771. Jewels and Stones”: This problem helps practice using sets or hashmaps with strings, which can be a useful data structure in encryption/decryption problems.

  5. “205. Isomorphic Strings”: This problem involves mapping one set of characters to another, which is a concept that can be used in simple encryption/decryption schemes.

  6. “8. String to Integer (atoi)”: This problem involves parsing a string and converting it to a number, which can be useful in problems that involve numerical encryption schemes.

  7. “541. Reverse String II”: This problem is about manipulating strings in more complex ways, which can be helpful for understanding how to implement encryption/decryption algorithms.

  8. “557. Reverse Words in a String III”: Similar to the previous problem, this is another problem that involves complex string manipulation.

  9. “136. Single Number”: This problem involves using XOR to find a single number in a list. XOR is a common operation in many encryption algorithms.

  10. “461. Hamming Distance”: This problem involves bitwise operations, which are often used in encryption/decryption problems.

Problem Classification

Problem Statement: 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:

For each character c in the string, we find the index i satisfying keys[i] == c in keys. 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:

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. 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.


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 1 <= 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.

Analyze the provided problem statement. Categorize it based on its domain, ignoring ‘How’ it might be solved. Identify and list out the ‘What’ components. Based on these, further classify the problem. Explain your categorizations.

Distilling the Problem to Its Core Elements

In order to have me distill a problem to its core, you could ask questions that prompt for a deeper analysis of the problem, understanding of the underlying concepts, and simplification of the problem’s essence. Here are some examples of such prompts:

  1. Can you identify the fundamental concept or principle this problem is based upon? Please explain.
  2. What is the simplest way you would describe this problem to someone unfamiliar with the subject?
  3. What is the core problem we are trying to solve? Can we simplify the problem statement?
  4. Can you break down the problem into its key components?
  5. What is the minimal set of operations we need to perform to solve this problem?

These prompts guide the discussion towards simplifying the problem, stripping it down to its essential elements, and understanding the core problem to be solved.

Visual Model of the Problem

How to visualize the problem statement for this problem?

Problem Restatement

Could you start by paraphrasing the problem statement in your own words? Try to distill the problem into its essential elements and make sure to clarify the requirements and constraints. This exercise should aid in understanding the problem better and aligning our thought process before jumping into solving it.

Abstract Representation of the Problem

Could you help me formulate an abstract representation of this problem?

Given this problem, how can we describe it in an abstract way that emphasizes the structure and key elements, without the specific real-world details?


Are there any specialized terms, jargon, or technical concepts that are crucial to understanding this problem or solution? Could you define them and explain their role within the context of this problem?

Problem Simplification and Explanation

Could you please break down this problem into simpler terms? What are the key concepts involved and how do they interact? Can you also provide a metaphor or analogy to help me understand the problem better?


Given the problem statement and the constraints provided, identify specific characteristics or conditions that can be exploited to our advantage in finding an efficient solution. Look for patterns or specific numerical ranges that could be useful in manipulating or interpreting the data.

What are the key insights from analyzing the constraints?

Case Analysis

Could you please provide additional examples or test cases that cover a wider range of the input space, including edge and boundary conditions? In doing so, could you also analyze each example to highlight different aspects of the problem, key constraints and potential pitfalls, as well as the reasoning behind the expected output for each case? This should help in generating key insights about the problem and ensuring the solution is robust and handles all possible scenarios.

Provide names by categorizing these cases

What are the key insights from analyzing the different cases?

Identification of Applicable Theoretical Concepts

Can you identify any mathematical or algorithmic concepts or properties that can be applied to simplify the problem or make it more manageable? Think about the nature of the operations or manipulations required by the problem statement. Are there existing theories, metrics, or methodologies in mathematics, computer science, or related fields that can be applied to calculate, measure, or perform these operations more effectively or efficiently?

Problem Breakdown and Solution Methodology

Given the problem statement, can you explain in detail how you would approach solving it? Please break down the process into smaller steps, illustrating how each step contributes to the overall solution. If applicable, consider using metaphors, analogies, or visual representations to make your explanation more intuitive. After explaining the process, can you also discuss how specific operations or changes in the problem’s parameters would affect the solution? Lastly, demonstrate the workings of your approach using one or more example cases.

Inference of Problem-Solving Approach from the Problem Statement

How did you infer from the problem statement that this problem can be solved using ?

Stepwise Refinement

  1. Could you please provide a stepwise refinement of our approach to solving this problem?

  2. How can we take the high-level solution approach and distill it into more granular, actionable steps?

  3. Could you identify any parts of the problem that can be solved independently?

  4. Are there any repeatable patterns within our solution?

Solution Approach and Analysis

Given the problem statement, can you explain in detail how you would approach solving it? Please break down the process into smaller steps, illustrating how each step contributes to the overall solution. If applicable, consider using metaphors, analogies, or visual representations to make your explanation more intuitive. After explaining the process, can you also discuss how specific operations or changes in the problem’s parameters would affect the solution? Lastly, demonstrate the workings of your approach using one or more example cases.

Thought Process

Explain the thought process by thinking step by step to solve this problem from the problem statement and code the final solution. Write code in Python3. What are the cues in the problem statement? What direction does it suggest in the approach to the problem? Generate insights about the problem statement.

From Brute Force to Optimal Solution

Could you please begin by illustrating a brute force solution for this problem? After detailing and discussing the inefficiencies of the brute force approach, could you then guide us through the process of optimizing this solution? Please explain each step towards optimization, discussing the reasoning behind each decision made, and how it improves upon the previous solution. Also, could you show how these optimizations impact the time and space complexity of our solution?

Code Explanation and Design Decisions

  1. Identify the initial parameters and explain their significance in the context of the problem statement or the solution domain.

  2. Discuss the primary loop or iteration over the input data. What does each iteration represent in terms of the problem you’re trying to solve? How does the iteration advance or contribute to the solution?

  3. If there are conditions or branches within the loop, what do these conditions signify? Explain the logical reasoning behind the branching in the context of the problem’s constraints or requirements.

  4. If there are updates or modifications to parameters within the loop, clarify why these changes are necessary. How do these modifications reflect changes in the state of the solution or the constraints of the problem?

  5. Describe any invariant that’s maintained throughout the code, and explain how it helps meet the problem’s constraints or objectives.

  6. Discuss the significance of the final output in relation to the problem statement or solution domain. What does it represent and how does it satisfy the problem’s requirements?

Remember, the focus here is not to explain what the code does on a syntactic level, but to communicate the intent and rationale behind the code in the context of the problem being solved.

Coding Constructs

Consider the following piece of complex software code.

  1. What are the high-level problem-solving strategies or techniques being used by this code?

  2. If you had to explain the purpose of this code to a non-programmer, what would you say?

  3. Can you identify the logical elements or constructs used in this code, independent of any programming language?

  4. Could you describe the algorithmic approach used by this code in plain English?

  5. What are the key steps or operations this code is performing on the input data, and why?

  6. Can you identify the algorithmic patterns or strategies used by this code, irrespective of the specific programming language syntax?

Language Agnostic Coding Drills

Your mission is to deconstruct this code into the smallest possible learning units, each corresponding to a separate coding concept. Consider these concepts as unique coding drills that can be individually implemented and later assembled into the final solution.

  1. Dissect the code and identify each distinct concept it contains. Remember, this process should be language-agnostic and generally applicable to most modern programming languages.

  2. Once you’ve identified these coding concepts or drills, list them out in order of increasing difficulty. Provide a brief description of each concept and why it is classified at its particular difficulty level.

  3. Next, describe the problem-solving approach that would lead from the problem statement to the final solution. Think about how each of these coding drills contributes to the overall solution. Elucidate the step-by-step process involved in using these drills to solve the problem. Please refrain from writing any actual code; we’re focusing on understanding the process and strategy.

Targeted Drills in Python

Now that you’ve identified and ordered the coding concepts from a complex software code in the previous exercise, let’s focus on creating Python-based coding drills for each of those concepts.

  1. Begin by writing a separate piece of Python code that encapsulates each identified concept. These individual drills should illustrate how to implement each concept in Python. Please ensure that these are suitable even for those with a basic understanding of Python.

  2. In addition to the general concepts, identify and write coding drills for any problem-specific concepts that might be needed to create a solution. Describe why these drills are essential for our problem.

  3. Once all drills have been coded, describe how these pieces can be integrated together in the right order to solve the initial problem. Each drill should contribute to building up to the final solution.

Remember, the goal is to not only to write these drills but also to ensure that they can be cohesively assembled into one comprehensive solution.


Similar Problems

Can you suggest 10 problems from LeetCode that require similar problem-solving strategies or use similar underlying concepts as the problem we’ve just solved? These problems can be from any domain or topic, but they should involve similar steps or techniques in the solution process. Also, please briefly explain why you consider each of these problems to be related to our original problem.