Category: C# Coding Test Tutorials

Hello! In this post, we will solve a coding test problem using the C# language. The topic is ‘Jumong’s Command’. This problem simulates the situation where Jumong issues commands and implements an algorithm to handle them efficiently. I will explain in detail how to solve the problem and implement the code.

Problem Description

Jumong gives commands to warriors before each battle. Each warrior performs their duties according to the commands they receive. The warriors interpret Jumong’s commands as follows:

• Warrior’s unique number (a positive integer starting from 1)
• Content of the command (indicates what action needs to be performed)

Jumong has N warriors and M commands. The commands are given in the following format:

    1. ATTACK A B  // Warrior A attacks warrior B
    2. DEFENSE A   // Warrior A assumes a defensive posture
    3. RETREAT A    // Warrior A retreats
    

If a warrior successfully performs their duty, the result should output ‘SUCCESS’, and if they fail, it should output ‘FAIL’. Warriors do not perform commands if they lose interest before executing the command. Interest decreases over time. If a warrior is in a situation where they cannot perform the command, ‘FAIL’ should be printed.

Input Format

The input is given in the following format:

    N (number of warriors)
    M (number of commands)
    Interest decay rate (0 ~ 1)
    Commands (M commands)
    

Output Format

The results are printed for each command. The results are listed in the same order as the commands.

Approach to the Problem

This problem requires an algorithm to process the given commands and determine whether each warrior can perform the commands. To solve the problem, I will consider the following steps:

1. Create a data structure to store the warriors and command lists.
2. Assume that each warrior initially has 100% interest.
3. Decrease the warrior’s interest according to the given interest decay rate, and process each command while updating their status.
4. Record success or failure based on the results of the commands.

Implementation

Code Example

The following is a C# implementation based on the above approach:

using System;
using System.Collections.Generic;

namespace JumongCommand
{
    class Warrior
    {
        public int Id { get; set; }
        public double Interest { get; set; }

        public Warrior(int id)
        {
            Id = id;
            Interest = 1.0; // 100% interest
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int M = int.Parse(Console.ReadLine());
            double interestDecayRate = double.Parse(Console.ReadLine());

            List warriors = new List();
            for (int i = 1; i <= N; i++)
            {
                warriors.Add(new Warrior(i));
            }

            List results = new List();
            for (int i = 0; i < M; i++)
            {
                string command = Console.ReadLine();
                string[] parts = command.Split(' ');

                if (parts[0] == "ATTACK")
                {
                    int attackerId = int.Parse(parts[1]);
                    int targetId = int.Parse(parts[2]);
                    ProcessAttack(warriors, results, attackerId, targetId);
                }
                else if (parts[0] == "DEFENSE")
                {
                    int defenderId = int.Parse(parts[1]);
                    ProcessDefense(warriors, results, defenderId);
                }
                else if (parts[0] == "RETREAT")
                {
                    int retreatId = int.Parse(parts[1]);
                    ProcessRetreat(warriors, results, retreatId);
                }

                // Apply interest decay
                foreach (var warrior in warriors)
                {
                    warrior.Interest -= interestDecayRate;
                    if (warrior.Interest < 0)
                        warrior.Interest = 0;
                }
            }

            foreach (var result in results)
            {
                Console.WriteLine(result);
            }
        }

        static void ProcessAttack(List warriors, List results, int attackerId, int targetId)
        {
            var attacker = warriors[attackerId - 1];
            var target = warriors[targetId - 1];

            if (attacker.Interest > 0)
            {
                results.Add("SUCCESS");
            }
            else
            {
                results.Add("FAIL");
            }
        }

        static void ProcessDefense(List warriors, List results, int defenderId)
        {
            var defender = warriors[defenderId - 1];

            if (defender.Interest > 0)
            {
                results.Add("SUCCESS");
            }
            else
            {
                results.Add("FAIL");
            }
        }

        static void ProcessRetreat(List warriors, List results, int retreatId)
        {
            var retreatingWarrior = warriors[retreatId - 1];

            if (retreatingWarrior.Interest > 0)
            {
                results.Add("SUCCESS");
            }
            else
            {
                results.Add("FAIL");
            }
        }
    }
}

Code Explanation

The code defines a ‘Warrior’ class to manage the state of each warrior. Each warrior has a unique ID and a current interest as properties. The main program reads the warrior list and command list in order and calls separate methods to process each command, updating the results.

Verification of Results

After the commands are completed, the result list is printed to confirm the final success or failure results. This is a simple implementation of how warriors execute commands and manage resources.

Test Cases

We can create several test cases to check if it works properly.

Example Input

5
3
0.1
ATTACK 1 2
DEFENSE 3
RETREAT 4

Expected Results

SUCCESS
SUCCESS
SUCCESS

By testing various inputs in this manner, we can check if the algorithm correctly responds to all situations.

Conclusion

In this post, we explored the process of solving the ‘Jumong’s Command’ problem. Understanding the structure and implementation of the algorithm, as well as building the logic for processing various commands, was important. I hope you continue to improve your skills through more algorithm problems. Thank you!

While preparing for coding tests or algorithm problem-solving, it is important to understand and learn approaches for various types of problems. Today, we will take an in-depth look at the problem of finding the sum of continuous elements.

Problem Description

We will examine the problem of calculating the sum of consecutive elements in a given integer array and finding the shortest continuous subarray that meets a specific criteria.

Problem Definition

Problem: Find the Sum of Consecutive Elements

Given an integer array nums and an integer target, 
return the length of the shortest continuous subarray whose sum is greater than or equal to target. 
If there is no such subarray, return 0.

Input Example:
nums = [2,3,1,2,4,3]
target = 7

Output Example:
2 (length of subarray [4,3])

Problem Solving Approach

To solve this problem, two main approaches can be used: brute force (exhaustive search) and the two-pointer (sliding window) method. Here, we will use the two-pointer method for an efficient solution.

Two-Pointer Approach

The two-pointer approach involves exploring the array using two pointers (left and right) to find the subarray that satisfies the desired condition. The advantage of this method is its time complexity of O(n), making it efficient.

Step-by-Step Solution

1. Initialization: Initialize the two pointers. Set the left pointer left to 0 and the right pointer right to 0. Also, initialize the current sum currentSum to 0 and the minimum length minLength to infinity.
2. Condition Check: Traverse the array using the right pointer and add nums[right] to currentSum. Then check if currentSum is greater than or equal to target.
3. Adjusting the Subarray: If currentSum is greater than or equal to target, update the minimum length and increase the left pointer while subtracting nums[left] from currentSum. This helps find the shortest possible subarray.
4. Termination Condition: Repeat this process until the right pointer reaches the end of the array.

Function Implementation

Now, let’s implement the above logic through C# code.

using System;

public class Solution {
    public int MinSubArrayLen(int target, int[] nums) {
        int left = 0;
        int currentSum = 0;
        int minLength = int.MaxValue;

        for (int right = 0; right < nums.Length; right++) {
            currentSum += nums[right];

            while (currentSum >= target) {
                minLength = Math.Min(minLength, right - left + 1);
                currentSum -= nums[left];
                left++;
            }
        }

        return minLength == int.MaxValue ? 0 : minLength;
    }
}

Code Explanation

The above C# code works as follows:

• Initial Variable Setup: Initialize left, currentSum, and minLength.
• Array Traversal: Traverse the array using the right variable and add the current element to currentSum.
• Condition Check: If currentSum is greater than or equal to target, update minLength and increase the left pointer while subtracting nums[left] from currentSum.
• Return Result: Finally, if minLength has not been updated, return 0; otherwise, return the found minimum length.

Example Test Cases

Now, let’s write some example test cases to test this function.

public static void Main(string[] args) {
    Solution sol = new Solution();
    
    Console.WriteLine(sol.MinSubArrayLen(7, new int[] { 2, 3, 1, 2, 4, 3 })); // Output: 2
    Console.WriteLine(sol.MinSubArrayLen(4, new int[] { 1, 4, 4 }));        // Output: 1
    Console.WriteLine(sol.MinSubArrayLen(11, new int[] { 1, 1, 1, 1, 1, 1 })); // Output: 0
    Console.WriteLine(sol.MinSubArrayLen(8, new int[] { 2, 3, 1, 2, 4, 3 })); // Output: 2
}

Conclusion

In this lecture, we learned the problem-solving approach using two pointers through the problem of finding the sum of consecutive elements. It is important to accurately understand the nature of a problem and choose the appropriate approach to solve algorithmic problems. In practice, solving various problems helps gain experience and become familiar with different algorithms, so continuous practice is encouraged.

Try to enhance your algorithmic sense by encountering and solving various problems!

In this session, we will solve algorithm problems for employment using C#. The topic will be based on a popular dance rhythm game called DDR (Dance Dance Revolution). We will implement the input patterns required in the DDR game in code and write an algorithm to process those patterns.

Problem Description

You are a developer analyzing the patterns of the DDR game. In DDR, input is received for each direction panel (up, down, left, right). The input consists of a series of directional key patterns given at specific time intervals. Each direction can be represented as follows:

• U: Up
• D: Down
• L: Left
• R: Right

Based on the given input pattern, you need to determine how accurately the user has inputted that pattern. We will check the length of the pattern and whether it was input correctly within a certain time frame to assign a score.

Input Format

• The first line contains the length of the pattern N. (1 ≤ N ≤ 100)
• The second line contains the pattern made up of N characters.
• The third line contains the user’s input pattern X.

Output Format

The accuracy score indicating how closely the user’s input matches the pattern will be output. The score is calculated as follows:

• Scores are calculated only when the length of the pattern and the user’s input length are the same.
• 10 points are awarded for each matching character.
• If there is a mismatch, the score will be lost at that index, and the penalty is 5 points.
• The final score is output.

Example Input

5
UDLRU
UDLRD

Example Output

35

Problem Solving Process

Now, let’s take a step-by-step look at how to write the code to solve this problem. First, we will outline the required functionality.

1. Declare variables to store the length of the pattern (N) and the input pattern.
2. Store the pattern in an array or list of length N.
3. Store the user’s input pattern in an array or list.
4. Compare the input pattern with the existing pattern to check for matches and calculate scores.
5. Output the final score.

Writing C# Code

Now, we will write the C# code according to the above requirements.

using System;

class DDR
{
    static void Main()
    {
        // Get the length of the pattern N
        int N = int.Parse(Console.ReadLine());
        
        // Declare string arrays to store the DDR pattern and user input pattern
        string pattern = Console.ReadLine();
        string userInput = Console.ReadLine();
        
        // Initialize score variable
        int score = 0;
        
        // Check if the input length is the same as the pattern
        if (N != userInput.Length)
        {
            Console.WriteLine("The input length does not match the pattern length.");
            return;
        }

        // Calculate scores by comparing the pattern and user input
        for (int i = 0; i < N; i++)
        {
            if (pattern[i] == userInput[i])
            {
                score += 10; // Award 10 points for each match
            }
            else
            {
                score -= 5; // Deduct 5 points for each mismatch
            }
        }
        
        // Output the final score
        Console.WriteLine(score);
    }
}

The code above is relatively simple, designed to receive the DDR pattern input and compare it with the user input to calculate the score. When executed, it prompts the user for the pattern and input, calculates the score, and outputs it.

Code Explanation

1. using System;: Declaration to use the basic library of C#.

2. class DDR: Defines a class named DDR.

3. static void Main(): The entry point of the program. All code execution starts here.

4. The user's input is taken using int.Parse(Console.ReadLine()) and stored in an integer variable N.

5. The pattern and user input are both received and stored as strings.

6. The score variable score is initialized.

7. It checks whether the length of the user's input matches the length of the pattern. If not, the program terminates.

8. The logic compares the pattern and awards 10 points for matches and deducts 5 points for mismatches.

9. Finally, it outputs the final score.

Conclusion

In this lecture, we structured an algorithm problem based on the DDR pattern and explored how to solve it using C#. We wrote logic for pattern analysis and score calculation through algorithm problem-solving. I hope this helps improve your current skills in algorithms and coding. Let's continue studying various topics together in the future.

In this lecture, we will learn how to solve the “Lowest Common Multiple (LCM)” problem, which is frequently asked in coding tests. The lowest common multiple refers to the smallest positive integer that is divisible by two or more numbers. This concept has mathematically significant properties and is often used in algorithmic problem-solving.

Problem Description

Write a program to find the lowest common multiple of two given positive integers A and B.

Problem-Solving Process

To solve the problem, we need to understand how to find the lowest common multiple. Generally, the lowest common multiple can be found using the Greatest Common Divisor (GCD). The lowest common multiple of two numbers A and B is expressed as follows:

LCM(A, B) = (A * B) / GCD(A, B)

Thus, to find the lowest common multiple, we simply divide the product of the two numbers by their greatest common divisor. Now, let’s implement this algorithm in C#.

Finding the Greatest Common Divisor

The greatest common divisor can be easily calculated using the Euclidean algorithm. The basic principle of the Euclidean algorithm is as follows:

GCD(A, B) = GCD(B, A % B) (Repeat until B becomes 0)

Now, let’s implement this in C#.

C# Code Implementation

using System;

class Program
{
    // Method to calculate the greatest common divisor
    static int GCD(int a, int b)
    {
        while (b != 0)
        {
            int temp = b;
            b = a % b;
            a = temp;
        }
        return a;
    }

    // Method to calculate the lowest common multiple
    static int LCM(int a, int b)
    {
        return (a * b) / GCD(a, b);
    }

    static void Main(string[] args)
    {
        Console.Write("Enter the first integer: ");
        int a = int.Parse(Console.ReadLine());
        
        Console.Write("Enter the second integer: ");
        int b = int.Parse(Console.ReadLine());

        Console.WriteLine($"The lowest common multiple is: {LCM(a, b)}.");
    }
}

The above code calculates and outputs the lowest common multiple of two integers entered by the user. The GCD method calculates the greatest common divisor, while the LCM method calculates the lowest common multiple.

Code Explanation

1. Greatest Common Divisor Method

The GCD(int a, int b) method takes two integers a and b as arguments and returns their greatest common divisor. It uses a while loop to repeat until b is 0, updating the values of a and b accordingly. This implements the Euclidean algorithm.

2. Lowest Common Multiple Method

The LCM(int a, int b) method calculates the lowest common multiple by dividing the product of the two numbers by their greatest common divisor and returning the result. Care must be taken to prevent integer overflow during this process.

3. Main Method

The Main method receives two integers from the user and uses the LCM method to display the result. Input is received through Console.ReadLine() and converted to an integer using int.Parse().

Testing and Exception Handling

The lowest common multiple program implemented in this lecture is simple, but it is important to consider a few exceptional cases. For example, if the user inputs 0 or a negative integer, methods to handle such inputs should be considered. To do this, we can add the following exception handling:

static void Main(string[] args)
{
    try
    {
        Console.Write("Enter the first integer: ");
        int a = int.Parse(Console.ReadLine());
        if (a <= 0) throw new ArgumentException("A positive integer must be entered.");

        Console.Write("Enter the second integer: ");
        int b = int.Parse(Console.ReadLine());
        if (b <= 0) throw new ArgumentException("A positive integer must be entered.");

        Console.WriteLine($"The lowest common multiple is: {LCM(a, b)}.");
    }
    catch (FormatException)
    {
        Console.WriteLine("Invalid input. Please enter an integer.");
    }
    catch (ArgumentException ex)
    {
        Console.WriteLine(ex.Message);
    }
    catch (Exception ex)
    {
        Console.WriteLine("An unknown error has occurred: " + ex.Message);
    }
}

In the above code, we use a try-catch block to handle various exceptions. When the user inputs invalid values, appropriate error messages are provided to prevent the program from terminating abnormally.

Efficiency and Optimization

The Euclidean algorithm used in this problem-solving process is designed to calculate the greatest common divisor very efficiently. This algorithm has a time complexity of O(log(min(A, B))), making it effective even for finding the least common multiple of very large numbers. In this regard, the performance of the algorithm is a very important factor.

Conclusion

In this lecture, we implemented an algorithm to find the least common multiple using C#. We understood the functionality of each method and discussed exception handling and efficiency. The least common multiple is applied in various problems, so it is important to familiarize yourself with this algorithm. I hope you continue to strengthen your skills by solving various algorithmic problems!

Thank you for reading this far. In the next lecture, we will explore other algorithm problem-solving methods.