Edit Distance
This is a classic one in computer science and is known as the Edit Distance problem. It’s used in various applications like spell correction and DNA sequence alignment. Here’s a simple explanation of the problem and a general approach to solving it:
Problem
You have two words, word1
and word2
, and you want to find the minimum number of operations to make word1
equal to word2
. You can use three types of operations:
 Insert a character: You can insert a character into
word1
.  Delete a character: You can delete a character from
word1
.  Replace a character: You can replace a character in
word1
with another character.
Solution
You can use dynamic programming to solve this problem efficiently. Here’s a stepbystep guide:
Create a Table: Create a table (2D array)
dp
with dimensions(len(word1) + 1) x (len(word2) + 1)
. This table will help store the solutions to subproblems.Initialize the Table: Initialize the first row and the first column of the table.
dp[i][0] = i
anddp[0][j] = j
, as it takesi
deletions to convert the firsti
characters ofword1
to an empty string, andj
insertions to convert an empty string to the firstj
characters ofword2
.Build the Solution: Iterate through the table, filling in each cell based on the following rules:
 If
word1[i1]
is equal toword2[j1]
, thendp[i][j] = dp[i1][j1]
. No operation is needed.  Otherwise, take the minimum of the following three operations and add 1:
dp[i1][j]
: This represents deleting a character fromword1
.dp[i][j1]
: This represents inserting a character intoword1
.dp[i1][j1]
: This represents replacing a character inword1
.
 If
Final Result: The value in the bottomright corner of the table,
dp[len(word1)][len(word2)]
, will be the minimum number of operations needed to convertword1
toword2
.
Example
Solution:


This code efficiently calculates the minimum number of operations needed to convert word1
to word2
, adhering to the constraints provided.
Identifying Problem Isomorphism
“Edit Distance” can be approximately mapped to “Delete Operation for Two Strings” (LeetCode #583).
Reasoning:
Both problems deal with sequences and involve transforming one sequence into another.
In “Edit Distance,” the task is to compute the minimum number of operations (insertions, deletions, and substitutions) required to transform one word into another.
In “Delete Operation for Two Strings,” the task is to find the minimum number of steps required to make two strings the same, where in each step you can delete one character in either string.
The common idea here is the transformation of one sequence into another using a minimum number of operations. Both problems involve a form of deletion operation to achieve this. The difference is that in the “Edit Distance” problem, you have additional operations (insertions and substitutions), whereas in the “Delete Operation for Two Strings” problem, you only have deletions.
This is an approximate mapping because while both problems share a similar concept, the allowable operations and exact objectives are not the same. You need to restrict the operations in the “Edit Distance” problem to only deletions to exactly map it to the “Delete Operation for Two Strings” problem.
10 Prerequisite LeetCode Problems
“72. Edit Distance” involves dynamic programming and string manipulation. Here are 10 problems to prepare:
70. Climbing Stairs: This is a classic dynamic programming problem that provides a good introduction to the concept.
509. Fibonacci Number: This problem also introduces the idea of dynamic programming.
53. Maximum Subarray: This problem is a slightly more complex example of dynamic programming.
746. Min Cost Climbing Stairs: Another variant of dynamic programming problems involving a simple decision at each step.
647. Palindromic Substrings: This problem combines string manipulation and dynamic programming.
516. Longest Palindromic Subsequence: This problem has similar themes to the Edit Distance problem, with string manipulation and dynamic programming.
392. Is Subsequence: This problem can be solved using two pointers or dynamic programming and involves string manipulation.
344. Reverse String: This problem provides practice with string manipulation.
387. First Unique Character in a String: This problem involves string manipulation and can be solved with a hash map or array.
680. Valid Palindrome II: This problem involves manipulating a string to check if it can become a palindrome.
These cover string manipulation and dynamic programming, which are the key skills needed for the Edit Distance problem.
Problem Analysis and Key Insights
What are the key insights from analyzing the problem statement?
Problem Boundary
What is the scope of this problem?
How to establish the boundary of this problem?
Problem Classification
Problem Statement:Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word:
Insert a character Delete a character Replace a character
Example 1:
Input: word1 = “horse”, word2 = “ros” Output: 3 Explanation: horse > rorse (replace ‘h’ with ‘r’) rorse > rose (remove ‘r’) rose > ros (remove ’e’)
Example 2:
Input: word1 = “intention”, word2 = “execution” Output: 5 Explanation: intention > inention (remove ’t’) inention > enention (replace ‘i’ with ’e’) enention > exention (replace ’n’ with ‘x’) exention > exection (replace ’n’ with ‘c’) exection > execution (insert ‘u’)
Constraints:
0 <= word1.length, word2.length <= 500 word1 and word2 consist of lowercase English letters.
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
Can you identify the fundamental concept or principle this problem is based upon? Please explain. What is the simplest way you would describe this problem to someone unfamiliar with the subject? What is the core problem we are trying to solve? Can we simplify the problem statement? Can you break down the problem into its key components? What is the minimal set of operations we need to perform to solve this problem?
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 realworld details?
Terminology
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?
Constraints
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 edge 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?
Simple Explanation
Can you explain this problem in simple terms or like you would explain to a nontechnical person? Imagine you’re explaining this problem to someone without a background in programming. How would you describe it? If you had to explain this problem to a child or someone who doesn’t know anything about coding, how would you do it? In layman’s terms, how would you explain the concept of this problem? Could you provide a metaphor or everyday example to explain the idea of this problem?
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 ProblemSolving Approach from the Problem Statement
Can you identify the key terms or concepts in this problem and explain how they inform your approach to solving it? Please list each keyword and how it guides you towards using a specific strategy or method.
How did you infer from the problem statement that this problem can be solved using ?
Simple Explanation of the Proof
I’m having trouble understanding the proof of this algorithm. Could you explain it in a way that’s easy to understand?
Stepwise Refinement
Could you please provide a stepwise refinement of our approach to solving this problem?
How can we take the highlevel solution approach and distill it into more granular, actionable steps?
Could you identify any parts of the problem that can be solved independently?
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.
Identify Invariant
What is the invariant in this problem?
Identify Loop Invariant
What is the loop invariant in this problem?
Thought Process
Can you explain the basic thought process and steps involved in solving this type of problem?
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.
Establishing Preconditions and Postconditions
Parameters:
 What are the inputs to the method?
 What types are these parameters?
 What do these parameters represent in the context of the problem?
Preconditions:
 Before this method is called, what must be true about the state of the program or the values of the parameters?
 Are there any constraints on the input parameters?
 Is there a specific state that the program or some part of it must be in?
Method Functionality:
 What is this method expected to do?
 How does it interact with the inputs and the current state of the program?
Postconditions:
 After the method has been called and has returned, what is now true about the state of the program or the values of the parameters?
 What does the return value represent or indicate?
 What side effects, if any, does the method have?
Error Handling:
 How does the method respond if the preconditions are not met?
 Does it throw an exception, return a special value, or do something else?
Problem Decomposition
Problem Understanding:
 Can you explain the problem in your own words? What are the key components and requirements?
Initial Breakdown:
 Start by identifying the major parts or stages of the problem. How can you break the problem into several broad subproblems?
Subproblem Refinement:
 For each subproblem identified, ask yourself if it can be further broken down. What are the smaller tasks that need to be done to solve each subproblem?
Task Identification:
 Within these smaller tasks, are there any that are repeated or very similar? Could these be generalized into a single, reusable task?
Task Abstraction:
 For each task you’ve identified, is it abstracted enough to be clear and reusable, but still makes sense in the context of the problem?
Method Naming:
 Can you give each task a simple, descriptive name that makes its purpose clear?
Subproblem Interactions:
 How do these subproblems or tasks interact with each other? In what order do they need to be performed? Are there any dependencies?
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
Identify the initial parameters and explain their significance in the context of the problem statement or the solution domain.
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?
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.
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?
Describe any invariant that’s maintained throughout the code, and explain how it helps meet the problem’s constraints or objectives.
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.
What are the highlevel problemsolving strategies or techniques being used by this code?
If you had to explain the purpose of this code to a nonprogrammer, what would you say?
Can you identify the logical elements or constructs used in this code, independent of any programming language?
Could you describe the algorithmic approach used by this code in plain English?
What are the key steps or operations this code is performing on the input data, and why?
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.
Dissect the code and identify each distinct concept it contains. Remember, this process should be languageagnostic and generally applicable to most modern programming languages.
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.
Next, describe the problemsolving 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 stepbystep 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 Pythonbased coding drills for each of those concepts.
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.
In addition to the general concepts, identify and write coding drills for any problemspecific concepts that might be needed to create a solution. Describe why these drills are essential for our problem.
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.
Q&A
Similar Problems
Can you suggest 10 problems from LeetCode that require similar problemsolving 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.