C# Coding Test Course, Calculating ATM Withdrawal Time

This course focuses on learning how to solve algorithm problems using C#. In particular, we will choose the topic “Calculating ATM Withdrawal Time” and explain the entire process from understanding the problem to finding the solution and writing the code in detail. Since this is a problem frequently encountered in real coding tests and interviews, this course will further enhance your algorithm problem-solving skills.

Problem Description

People line up to withdraw cash from the bank’s ATM machine. The time taken for each person to make a withdrawal may vary. The goal of this problem is to calculate the total withdrawal time when N people are waiting in line at the ATM. The following conditions are given:

  • The first person begins to withdraw in order.
  • Each person’s withdrawal can start only after the previous person’s withdrawal is complete.
  • The withdrawal times for each person are provided as an array.

For example, suppose the withdrawal times are [3, 1, 4, 3, 2]. The third person can only withdraw after the second person’s withdrawal is finished, so the total withdrawal time is:

3 (1st) + 1 (2nd) + 4 (3rd) + 3 (4th) + 2 (5th) = 13

Input and Output Format

Input

The first line contains an integer N (1 ≤ N ≤ 1000). The second line provides each person’s withdrawal time H1, H2, …, HN (1 ≤ Hi ≤ 1000), separated by spaces.

Output

Output the total time taken for all individuals to complete their withdrawals.

Problem-Solving Approach

To solve this problem, we can approach it in several steps:

1. **Understanding the Problem**: First, we need to confirm that each person’s withdrawal time is added sequentially when making a withdrawal.
2. **Choosing the Data Structure**: Since withdrawal times are provided as an array, it is most suitable to use an array to compute the time sum.
3. **Choosing the Algorithm**: Since each withdrawal time is summed sequentially, we can calculate the total withdrawal time simply using a loop.

Code Writing

Based on the above approach, let’s write C# code. The code can be written as follows:


using System;

class Program
{
    static void Main()
    {
        // Input the number of people N
        int N = Convert.ToInt32(Console.ReadLine());
        // Create an array for withdrawal times
        int[] withdrawalTimes = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);

        // Initialize the total withdrawal time variable
        int totalTime = 0;

        // Sum each person's withdrawal time
        foreach (var time in withdrawalTimes)
        {
            totalTime += time;
        }

        // Output the result
        Console.WriteLine(totalTime);
    }
}

Code Explanation and Analysis

The above C# code is structured as follows:

1. **Receiving Input**: Using `Console.ReadLine()` to input the number of people N in the first line and the withdrawal times in the second line.
2. **Array Conversion**: Converts the space-separated withdrawal times into an integer array using the `Array.ConvertAll` method.
3. **Total Time Calculation**: A foreach loop is used to add each person’s withdrawal time to the `totalTime` variable.
4. **Output the Result**: Finally, outputs the total withdrawal time.

Performance Analysis

The time complexity of the above algorithm is O(N), where N is the number of people making withdrawals. Since the process involves simply traversing all inputs and summing up the withdrawal times, it is very efficient. The space complexity is also O(N) as it requires an array to store the given withdrawal times.

Test Cases

Let’s create some test cases to validate the code:

  • Input: 
    5
3 1 4 3 2

    Output: 13

  • Input: 
    4
10 20 10 30

    Output: 70

  • Input: 
    3
1 1 1

    Output: 3

Conclusion

In this course, we learned a method to enhance our C# algorithm problem-solving skills through the problem of calculating ATM withdrawal time. The process of clearly understanding the problem and efficiently implementing it in code is crucial in coding tests. We encourage you to continue solving various algorithm problems to improve your skills. Thank you!