Read N Characters Given read4 II - Call Multiple Times

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class Solution:
    def __init__(self):
        self.buffPtr = 0
        self.buffCnt = 0
        self.buff = [''] * 4

    def read(self, buf: List[str], n: int) -> int:
        ptr = 0
        while ptr < n:
            if self.buffPtr == 0:
                self.buffCnt = read4(self.buff)
            if self.buffCnt == 0:
                break
            while ptr < n and self.buffPtr < self.buffCnt:
                buf[ptr] = self.buff[self.buffPtr]
                ptr += 1
                self.buffPtr += 1
            if self.buffPtr >= self.buffCnt:
                self.buffPtr = 0
        return ptr

10 Prerequisite LeetCode Problems

“158. Read N Characters Given Read4 II - Call Multiple Times” involves understanding of system design, file systems, and string manipulation.

Here are ten simpler problems:

“157. Read N Characters Given Read4” - This is a simplified version of the problem that does not involve multiple calls.
“344. Reverse String” - This problem practices simple manipulation of character arrays.
“415. Add Strings” - This problem provides practice for string manipulation in the context of simulating addition.
“186. Reverse Words in a String II” - This problem involves manipulating character arrays in-place, which is a key technique in the problem.
“67. Add Binary” - This problem is about string manipulation and simulating the binary addition process.
“125. Valid Palindrome” - This problem provides practice for checking and comparing characters in a string.
“8. String to Integer (atoi)” - This problem involves converting a string to an integer, handling different edge cases.
“387. First Unique Character in a String” - This problem is about counting character occurrences in a string.
“3. Longest Substring Without Repeating Characters” - This problem practices working with substrings and maintaining a sliding window.
“14. Longest Common Prefix” - This problem practices comparing characters in different strings.

Problem Classification

MORE DOWNVOTES THAN UPVOTES

Problem Statement:Given a file and assume that you can only read the file using a given method read4, implement a method read to read n characters. Your method read may be called multiple times.

Method read4:

The API read4 reads four consecutive characters from file, then writes those characters into the buffer array buf4.

The return value is the number of actual characters read.

Note that read4() has its own file pointer, much like FILE *fp in C.

Definition of read4:

Parameter:  char[] buf4
Returns:    int

buf4[] is a destination, not a source. The results from read4 will be copied to buf4[]. Below is a high-level example of how read4 works:

File file(“abcde”); // File is “abcde”, initially file pointer (fp) points to ‘a’ char[] buf4 = new char[4]; // Create buffer with enough space to store characters read4(buf4); // read4 returns 4. Now buf4 = “abcd”, fp points to ’e' read4(buf4); // read4 returns 1. Now buf4 = “e”, fp points to end of file read4(buf4); // read4 returns 0. Now buf4 = “”, fp points to end of file

Method read:

By using the read4 method, implement the method read that reads n characters from file and store it in the buffer array buf. Consider that you cannot manipulate file directly.

The return value is the number of actual characters read.

Definition of read:

Parameters:	char[] buf, int n
Returns:	int

buf[] is a destination, not a source. You will need to write the results to buf[]. Note:

Consider that you cannot manipulate the file directly. The file is only accessible for read4 but not for read. The read function may be called multiple times. Please remember to RESET your class variables declared in Solution, as static/class variables are persisted across multiple test cases. Please see here for more details. You may assume the destination buffer array, buf, is guaranteed to have enough space for storing n characters. It is guaranteed that in a given test case the same buffer buf is called by read.

Example 1:

Input: file = “abc”, queries = [1,2,1] Output: [1,2,0] Explanation: The test case represents the following scenario: File file(“abc”); Solution sol; sol.read(buf, 1); // After calling your read method, buf should contain “a”. We read a total of 1 character from the file, so return 1. sol.read(buf, 2); // Now buf should contain “bc”. We read a total of 2 characters from the file, so return 2. sol.read(buf, 1); // We have reached the end of file, no more characters can be read. So return 0. Assume buf is allocated and guaranteed to have enough space for storing all characters from the file. Example 2:

Input: file = “abc”, queries = [4,1] Output: [3,0] Explanation: The test case represents the following scenario: File file(“abc”); Solution sol; sol.read(buf, 4); // After calling your read method, buf should contain “abc”. We read a total of 3 characters from the file, so return 3. sol.read(buf, 1); // We have reached the end of file, no more characters can be read. So return 0.

Constraints:

1 <= file.length <= 500 file consist of English letters and digits. 1 <= queries.length <= 10 1 <= queries[i] <= 500

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.

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?

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.

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 ?

Could you please provide a stepwise refinement of our approach to solving this problem?
How can we take the high-level 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

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?

Coding Constructs

Consider the following piece of complex software code.

What are the high-level problem-solving strategies or techniques being used by this code?
If you had to explain the purpose of this code to a non-programmer, 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 language-agnostic 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 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.

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 problem-specific 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.