Learning Exercise
There are three primary types of loop constructs in Swift: while loops, repeat-while loops, and for-in loops.
While loops in Swift have the following structure:
while boolean-expression {
loop-body
}
The loops begin by first evaluating a Boolean expression. If the expression evaluates to false, then the body of the loop is skipped and execution begins on the first line following the loop. If the condition evaluates to true, then the body of the loop is executed, after which the Boolean expression is evaluated again, repeating this way until the Boolean expression evaluates to false.
var count = 3
while count > 0 {
print("\(count)…")
count -= 1
}
print("Liftoff!")
// prints:
// 3…
// 2…
// 1…
// Liftoff!
Repeat-while loops are similar to while loops, however, these loops differ in that the Boolean expression appears, and is evaluated, after the body of the loop is executed. As a result, these loops always execute at least once.
repeat {
print("This runs at least once")
} while false
print("Loop done")
// prints:
// This runs at least once
// Loop done
For-in loops are used to iterate over a sequence of values, taking each element in turn, binding it to a variable or constant name of the developer's choosing, then executes a block of code that may refer to the element. When every element of the sequence has been iterated over, the loop exits and execution begins with the first line following the body of the loop.
let numbers = [3, 10, 7, 11]
for number in numbers {
print("\(number) / 2 = \(number / 2)")
}
print("Done with numbers")
// prints:
// 3 / 2 = 1
// 10 / 2 = 5
// 7 / 2 = 3
// 11 / 2 = 5
// Done with numbers
Sometimes it is necessary to skip to the next iteration of a loop early, without completing the rest of the statements in the current iteration of the loop. The continue keyword can be used for this. When continue is executed, the loop jump to the next check to see if the next iteration of the loop can be run, i.e. the while in while and repeat-while loops or the check if there's another element in the sequence in for-in loops.
count = 1
repeat {
count += 1
if count == 4 { continue }
print(count)
} while count !=4 && count < 6
prints:
2
3
rather than:
2
3
5
6
You are a master mixologist, making tasty drinks for the public to enjoy on their nights out. But you figured that you could make your life easier by writing a bit of code to help you with your job.
Different drinks take different amount of time to prepare: "beer", "soda", and "water" take 0.5 minutes each, "shot"s take 1.0 minutes, "mixed drink"s take 1.5 minutes, "fancy drink"s take 2.5 minutes and "frozen drink"s take 3.0 minutes.
Implement the function timeToPrepare(drinks: [String]) -> Double which takes a non-empty array of drinks and returns the total time required to make the order.
timeToPrepare(drinks: ["beer", "frozen drink", "shot"])
// => 4.5
One of the first things you need to do when you start your shift is to make sure your little bin of lime wedges is full for the shift ahead. Implement the function makeWedges(needed: Int, limes: [String]) -> Int, which takes the number of lime wedges you need to cut and an array representing the supply of whole limes you have on hand. You can get 6 wedges from a "small" lime, 8 wedges from a "medium" lime and 10 from a "large" lime. While you still need more wedges and you still have more limes to cut up, take the first lime out of the array, and subtract the appropriate number of wedges from the amount you need. Keep going until you don't need any more wedges or you run out of limes.
Return the number of limes you cut up.
makeWedges(needed: 25, limes: ["small", "small", "large", "medium", "small"])
// => 4
Congratulations! Your long work day is nearly done and you will soon be going home to work on your new app. But you still have a stream of drink orders to make before you can hand off the orders to the next shift and leave.
Implement the function finishShift(minutesLeft: Int, remainingOrders: [[String]]) -> [[String]] which takes in the number of minutes left in your shift (guaranteed to be greater than 0), and a non-empty array of drink orders. As long as you still have time left in your shift you are to make the first order in the Array and then remove that order from the array. You can then subtract the amount of time it took to prepare that order, according to your function timeToPrepare(drinks:) from the time left on your shift. Your function should return the array of orderes that you have not yet gotten to before the end of your shift.
And good news! If you make all of the orders with time left on your shift you get to go home early!
finishShift(minutesLeft: 5, remainingOrders: [["beer", "frozen drink", "shot"], ["fancy drink", "soda"], ["beer", "beer", "water"], ["mixed drink", "frozen drink"]])
// => [["beer", "beer", "water"], ["mixed drink", "frozen drink"]]
In order to make sure the beer and soda stay fresh, you need to track their orders along with the times those orders were placed.
Implement the function orderTracker(orders: [(drink: String, time: String)]) -> (beer: (first: String, last: String, total: Int)?, soda: (first: String, last: String, total: Int)?) which, when given a list of orders and times return a pair of optional tuples containing the times of the first and last orders of beer and soda along with the total number of orders of each and nil if no orders for those beverages were made. You do not need to track any other drinks.
orderTracker(orders: [(drink: "beer", time: "10:01"), (drink: "frozen drink", time: "10:02"), (drink: "shot", time: "10:05"), (drink: "fancy drink", time: "10:06"), (drink: "soda", time: "10:09"), (drink: "beer", time: "10:15"), (drink: "beer", time: "10:22"), (drink: "water", time: "10:26"), (drink: "mixed drink", time: "10:28"), (drink: "frozen drink", time: "10:33")]
// => (beer: (first "10:01", last "10:22", total 3), soda: (first "10:09", last "10:09", total 1))
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