test.kt

data class Time(var hours: Int, var mins: Int) {
    operator fun plus(time: Time): Time {
        val minutes = this.mins + time.mins
        val hoursInMinutes = minutes / 60
        val remainingMinutes = minutes % 60
        val hours = this.hours + time.hours + hoursInMinutes
        return Time(hours, remainingMinutes)
    }
    
    operator fun minus(time: Time): Time {
        var hoursToRemove = 0
        var minutes = this.mins - time.mins
        if (minutes < 0) {
            minutes = minutes + 60
            hoursToRemove = 1
        }
            
        var hours = this.hours - time.hours - hoursToRemove
        if (hours < 0) hours = 0
        
        return Time(hours, minutes)
    }
    
    operator fun inc(): Time {
        if (this.mins + 1 == 61) {
            this.hours = this.hours + 2
            this.mins = 0
            return Time(this.hours, this.mins)
        } else {
            this.hours++
            this.mins++
            return Time(this.hours, this.mins)
        }
    }
    
    operator fun dec(): Time {
        if (this.mins - 1 == -1) {
            this.hours = this.hours - 2
            this.mins = 59
            return Time(this.hours, this.mins)
        } else {
            this.hours--
            this.mins--
            return Time(this.hours, this.mins)
        }
    }
}

fun main(args: Array<String>) {
    var newTime = Time(10, 40) + Time(3, 20)
    println(newTime) // => Time(hours=14, mins=0)
    println(newTime--) // => Time(hours=12, mins=59)
    
    val time = Time(10, 10) - Time(1, 60)
    println(time) // => Time(hours=8, mins=10)
}