C# Coding Test Course, Card Sorting

Problem Definition

The definition of the problem is as follows.

There are N cards given. Each card is represented by a unique integer from 1 to N. The task is to implement an algorithm that sorts these cards in ascending order. However, instead of a fixed sorting algorithm, we need to find the optimal method during the sorting process.

Problem Solving Process

Step 1: Problem Analysis

The first step in solving the problem is to analyze it closely. Given the number of cards N, we need to think about how to sort the data. If the number of cards is small, we can use simple direct methods (like bubble sort, selection sort, etc.), but when the numbers become larger, we should choose a more efficient algorithm.

Step 2: Algorithm Selection

Efficient sorting algorithms such as Quick Sort or Merge Sort can be considered. These sorting algorithms typically have an average time complexity of O(N log N), allowing them to handle large numbers of cards quickly.

Step 3: Implementation

Now, let’s implement a sorting algorithm in C#. Below is an example code implementing Merge Sort.

using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        int[] cards = { 5, 3, 8, 1, 2, 7 };

        Console.WriteLine("Cards before sorting: " + string.Join(", ", cards));
        cards = MergeSort(cards);
        Console.WriteLine("Cards after sorting: " + string.Join(", ", cards));
    }

    static int[] MergeSort(int[] array)
    {
        if (array.Length <= 1)
            return array;

        int midPoint = array.Length / 2;
        int[] left = MergeSort(array.Take(midPoint).ToArray());
        int[] right = MergeSort(array.Skip(midPoint).ToArray());

        return Merge(left, right);
    }

    static int[] Merge(int[] left, int[] right)
    {
        int[] result = new int[left.Length + right.Length];
        int leftIndex = 0, rightIndex = 0, resultIndex = 0;

        while (leftIndex < left.Length && rightIndex < right.Length)
        {
            if (left[leftIndex] <= right[rightIndex])
            {
                result[resultIndex++] = left[leftIndex++];
            }
            else
            {
                result[resultIndex++] = right[rightIndex++];
            }
        }

        while (leftIndex < left.Length)
        {
            result[resultIndex++] = left[leftIndex++];
        }

        while (rightIndex < right.Length)
        {
            result[resultIndex++] = right[rightIndex++];
        }

        return result;
    }
}

The above code implements a function that sorts cards using Merge Sort. It is designed to display the state of the cards before and after sorting.

Step 4: Testing

After writing the code, we need to check the accuracy and performance of the algorithm through various test cases. For example, one can consider scenarios such as when there is only one card, when all cards have the same number, and when the cards are sorted in reverse order.

static void TestSort()
{
    int[] testCards1 = { 4, 3, 2, 1 };
    int[] sortedCards1 = MergeSort(testCards1);
    Console.WriteLine("Cards after sorting 1: " + string.Join(", ", sortedCards1));  // 1, 2, 3, 4

    int[] testCards2 = { 1, 1, 1, 1 };
    int[] sortedCards2 = MergeSort(testCards2);
    Console.WriteLine("Cards after sorting 2: " + string.Join(", ", sortedCards2));  // 1, 1, 1, 1

    int[] testCards3 = { 3, 5, 2, 8, 7 };
    int[] sortedCards3 = MergeSort(testCards3);
    Console.WriteLine("Cards after sorting 3: " + string.Join(", ", sortedCards3));  // 2, 3, 5, 7, 8
}

Through this process, we can confirm that the given cards are sorted correctly.

Step 5: Optimization and Improvement

Once all implementations are completed, it’s necessary to optimize the performance of the code. In C#, using LINQ can make the code more concise, but it’s often implemented manually to consider performance issues. Additionally, utilizing multidimensional arrays or other data structures can reduce unnecessary resource consumption.