C# Coding Test Course, Finding the Minimum Number of Coins

Hello, everyone preparing for the coding test! In this course, we will solve an algorithm problem titled “Finding the Minimum Number of Coins,” and I will explain the detailed solution process. This problem will greatly help you understand algorithms and develop logical thinking.

Problem Definition

To purchase items at a store, a specific amount of money is required. However, we may have limitations on the types and quantities of coins we possess. The goal of this problem is to find a way to minimize the number of coins used to create a specific amount using the available coin denominations.

Problem Description

Here is an example of the problem:

  • Available coin denominations: 1 won, 5 won, 10 won, 50 won, 100 won
  • Target amount: 125 won

In this case, we need to find a way to make 125 won with the minimum number of coins.

Problem Approach

This problem is a typical greedy algorithm problem. A greedy algorithm solves a problem by making the best choice at each step.

Principle of Greedy Algorithm

  1. Use the largest coin available as much as possible.
  2. Repeat the same process for the remaining amount.

Problem Solving Steps

The specific steps for solving the problem are as follows:

  1. Initialize the types of coins and the amount.
  2. Proceed by sorting and using larger coins first.
  3. Count the number of each coin while reducing the amount.
  4. Repeat this until the remaining amount is 0.

C# Code Implementation

Now, let’s implement the C# code based on the above approach.


using System;

class Program
{
    static void Main(string[] args)
    {
        // Types of coins
        int[] coins = new int[] { 100, 50, 10, 5, 1 };
        // Target amount
        int targetAmount = 125;
        
        // Number of coins
        int totalCoins = 0;

        // Making amount with coins
        for (int i = 0; i < coins.Length; i++)
        {
            // Maximum number of coins that can be used
            while (targetAmount >= coins[i])
            {
                targetAmount -= coins[i];
                totalCoins++;
            }
        }

        // Output result
        Console.WriteLine("Minimum number of coins: " + totalCoins);
    }
}

Code Explanation

  • First, the required types of coins are initialized in an array.
  • The amount to be used is stored in a variable, and the totalCoins variable is declared to count the number of coins.
  • For each coin, if the amount is greater than the coin’s value, the coin is used, and the coin count is increased.
  • Finally, the minimum number of coins is printed to the console.

Code Execution Result

Running the above code will produce the following result:


Minimum number of coins: 3

We can see that at least 3 coins must be used to create 125 won with the given combinations of coins. For example, using one 100 won coin, one 5 won coin, and one 1 won coin would yield a valid combination.

Summary of the Problem-Solving Process

  • Understand the requirements of the problem accurately.
  • Select an appropriate algorithm (greedy).
  • Sequentially solve the problem while ensuring reliable results through the iterative process.
  • Once solved, review the efficiency and check for areas of improvement.

Conclusion

In this course, we learned the concept and application of greedy algorithms through the “Finding the Minimum Number of Coins” problem. I hope solving this problem has helped you improve your algorithmic thinking. Continue to face various problems to gain experience and grow as a better algorithm developer!

Thank you for participating in the C# coding test course. If you have any questions or would like to know more, please leave a comment!