Counting Minutes Explained

Solution

To solve this problem, you need to divide the problem into two parts:

• The first part is to convert hours to minutes.
• The second part is to calculate the difference between two times.

Let's dive into the first part

First things first, we’ll create convertHoursToMinutes(str:) function to return the number of hours in minutes.

func convertHoursToMinutes(str: String) -> Int {
        
        let timeSplit = str.split(separator: ":")
        guard let hr = Int(timeSplit[0]) else { return 0 }
        
        let a = str.suffix(2)
        
        var min = 0
        if a == "am" {
           min = hr * 60
        } else {
            min = (12 * 60) + (hr * 60)
        }
        
        guard let restMins = Int(timeSplit[1].prefix(2)) else { return 0 }
        min += restMins
        
        return min
    }

So if the str is 10:00am, it’ll return 720 minutes, but if the str is 10:00pm, it’ll return 1320 minutes. You can also count the rest of minutes if the time is like 10:30am or so.

But let’s back to the code, and explain how I did that.

First off, you’ll split the time into two sides: the left-most side representing hours, and the right side representing minutes. You can split them separately by a colon using split function.

To extract the hours side from timeSplit array, you can do that by the indexing into an array of strings.

Note: Don’t forget to convert the Substring into Int to use it in the mathematical operation.

So if you have this time [10:00am], it’ll extract the hours side, and get 10.

With a 12-hour standard, you need to check out if the time is am or pm. To get the right-most side of the time, you can do that by calling suffix function, and return the last two characters from timeSplit array.

Now that it’s time to compare if a is am or pm. If it’s am, you’ll multiply hours by 60 to convert it into minutes. If it’s pm, you’ll need to add midday which estimates 12 hours, and convert these hours into minutes.

To get the rest of minutes if exists. You’ll find them at the first part of right side of timeSplit array, and add them to the converting hours to minutes.

Now that you converted the hours into minutes.

Let's go to the second part

Back to the the main function countingMinutes(str:). You have this string 10:00am-9:00pm which expresses two different times, and you need to count the total minutes between them. So first split the two times individually by a hyphen/dash/minus using split(separator:) as well. To access the first/second time of timesSplit array you need to use the index as subscript on the timesSplit array variable, and convert this time from the Substring to String. By doing that you can use convertHoursToMinutes(str:) function to get the minutes from the first time, and the second time as well.

Now that you need to check if the first time is less than the second one. If so, then get the difference between them by subtracting the first time from the second time. Otherwise the first time has more minutes than the second one, so you’ll need to measure the whole day in minutes, and subtract the first time from the whole day to estimate how many minutes that remain in the day, and then add the next day which represents second time in minutes.

func countingMinutes(str: String) {

        let timesSplit = str.split(separator: "-")
        
        let firstTime = String(timesSplit[0])
        let secondTime = String(timesSplit[1])
        
        let firstTimeInMins = convertHoursToMinutes(str: firstTime)
        let secondTimeInMins = convertHoursToMinutes(str: secondTime)
        
        var minsCount = 0
        // Get the difference of minutes
        if firstTimeInMins < secondTimeInMins {
            minsCount = secondTimeInMins - firstTimeInMins
        } else {
            // Subtract the rest of the day
            minsCount = ((24 * 60) - (firstTimeInMins)) + secondTimeInMins
        }
        
        print(minsCount)
    }

Test cases