Swift Coding Test Course, Calculating ATM Withdrawal Time

Hello! In this article, we will cover a useful algorithm problem for preparing for coding tests, which is calculating the ATM withdrawal time. Through this problem, we will go step by step in solving it using arrays, sorting, and basic mathematical reasoning.

Problem Description

There are people lined up to withdraw money from an ATM. Each person knows the time (in seconds) it takes to use the ATM. Everyone will use the ATM in order of their line up. You need to write a program to calculate the total time taken for everyone to use the ATM.

In other words, when given an input like the following:

  • Input: [3, 1, 4, 3, 2]
  • Output: 32

If the first person takes 3 seconds, the second person takes 1 second, the third takes 4 seconds, and so on, the total time taken for everyone to use the ATM would be 3 + (3 + 1) + (3 + 1 + 4) + (3 + 1 + 4 + 3) + (3 + 1 + 4 + 3 + 2) = 32 seconds.

Approach to the Problem

To solve this problem, you can follow these steps:

  1. Sort the times taken in ascending order.
  2. Accumulate each person’s withdrawal time to calculate the total withdrawal time.

Implementation Steps

Step 1: Define and Sort Input

First, let’s sort the given times so that the fastest withdrawal times come first. To do this, we can use Swift’s sort() method.

let withdrawalTimes = [3, 1, 4, 3, 2]
let sortedTimes = withdrawalTimes.sorted()

Step 2: Calculate Total Time

Now, let’s use the sorted array to calculate the cumulative time based on each person’s withdrawal order.

var totalTime = 0
var accumulatedTime = 0

for time in sortedTimes {
    accumulatedTime += time
    totalTime += accumulatedTime
}

Step 3: Complete Code

Combining all the steps, the Swift program can be written as follows:

func calculateTotalWithdrawalTime(withdrawalTimes: [Int]) -> Int {
    let sortedTimes = withdrawalTimes.sorted()
    var totalTime = 0
    var accumulatedTime = 0

    for time in sortedTimes {
        accumulatedTime += time
        totalTime += accumulatedTime
    }
    
    return totalTime
}

let times = [3, 1, 4, 3, 2]
let total = calculateTotalWithdrawalTime(withdrawalTimes: times)
print("Total withdrawal time: \(total) seconds")

Code Explanation

The above code first receives a list of withdrawal times and sorts it, then uses a for loop to accumulate each user’s time and calculate the total time. Let’s take a closer look at each step.

  • calculateTotalWithdrawalTime(withdrawalTimes: [Int]) -> Int: A function that takes withdrawal times as input and returns the total time taken.
  • let sortedTimes = withdrawalTimes.sorted(): Sorts the array in ascending order using Swift’s sort feature.
  • accumulatedTime += time: Accumulates each person’s withdrawal time for calculation.
  • totalTime += accumulatedTime: Adds the accumulated time to the total time.

Results Confirmation

When the above code is executed, it will output that the total withdrawal time for the given times [3, 1, 4, 3, 2] is 32 seconds.

This method allows for sufficient testing with various inputs. For example:

let testTimes = [2, 5, 3, 1, 4]
let testTotal = calculateTotalWithdrawalTime(withdrawalTimes: testTimes)
print("Test withdrawal time: \(testTotal) seconds")

This will produce results corresponding to the test case.

Conclusion

In this article, we explored the process of solving the ATM withdrawal time calculation problem. This problem is a great example for practicing the basics of handling arrays, sorting, and calculating cumulative sums. Implementing the problem in Swift has deepened my understanding of the algorithm. It’s important to practice various problems of this level while preparing for coding tests.

I hope this has been helpful in your coding test preparations. If you have additional questions or problems, feel free to leave them in the comments!