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Learning Exercise
There are basically two types of loops:
Both are possible in Julia, though the second may be more common.
while loopFor open-ended problems where the number of times round the loop is unknown in advance, Julia has the while loop.
The basic form is fairly simple:
while condition
do_something()
end
In this case, the program will keep going round the loop until condition is no longer true.
Two ways to exit the loop early are available:
break causes the loop to exit, with execution continuing at the next line after the loop end.return x stops execution of the current function, passing the return value x back to the caller.With these options available, it can sometimes be convenient to create an "infinite" loop with while true ... end, then rely on finding a stopping condition within the loop body to trigger a break or return.
The simplest illustration is to loop over a range.
If we want to do something 10 times:
for n in 1:10
do_something(n)
end
If the current iteration fails to satisfy some condition, it is possible to skip immediately to the next iteration with a continue:
for n in 1:10
if is_useless(n)
continue
end
# we decided this iteration could be useful
do_something_slow(n)
end
In a shorter form, the if block could be replaced by is_useless(n) && continue.
Many other collection types can be looped over: elements in an array, characters in a string, keys in a dictionary...
The examples so far loop over the range 1:10, where the value is also the loop index.
More generally, the index may be needed and not just the value.
For this, the eachindex() function is used, for example for i in eachindex(my_array) ... end.
Your friend Li Mei runs a juice bar where she sells delicious mixed fruit juices. You are a frequent customer in her shop and realized you could make your friend's life easier. You decide to use your coding skills to help Li Mei with her job.
Li Mei likes to tell her customers in advance how long they have to wait for a juice from the menu that they ordered.
She has a hard time remembering the exact numbers because the time it takes to mix the juices varies.
"Pure Strawberry Joy" takes 0.5 minutes, "Energizer" and "Green Garden" take 1.5 minutes each, "Tropical Island" takes 3 minutes and "All or Nothing" takes 5 minutes.
For all other drinks (e.g., special offers) you can assume a preparation time of 2.5 minutes.
To help your friend, write a function time_to_mix_juice that takes a juice from the menu as an argument and returns the number of minutes it takes to mix that drink.
julia> time_to_mix_juice("Tropical Island")
3
julia> time_to_mix_juice("Berries & Lime")
2.5
A lot of Li Mei's creations include lime wedges, either as an ingredient or as part of the decoration. So when she starts her shift in the morning she needs to make sure the bin of lime wedges is full for the day ahead.
Implement the function limes_to_cut which takes the number of lime wedges Li Mei needs to cut and an array representing the supply of whole limes she has at hand.
She can get 6 wedges from a "small" lime, 8 wedges from a "medium" lime and 10 from a "large" lime.
She always cuts the limes in the order in which they appear in the list, starting with the first item.
She keeps going until she reached the number of wedges that she needs or until she runs out of limes.
Li Mei would like to know in advance how many limes she needs to cut.
The limes_to_cut function should return the number of limes to cut.
julia> limes_to_cut(25, ["small", "small", "large", "medium", "small"])
4
Li Mei likes to keep track of how long it will take to mix the orders customers are waiting for.
Implement the order_times function, which takes a queue of orders and returns a vector of times to mix.
julia> order_times(["Energizer", "Tropical Island"])
[1.5, 3.0]
Li Mei always works until 3pm. Then her employee Dmitry takes over. There are often drinks that have been ordered but are not prepared yet when Li Mei's shift ends. Dmitry will then prepare the remaining juices.
To make the hand-over easier, implement a function remaining_orders which takes the number of minutes left in Li Mei"s shift and an array of juices that have been ordered but not prepared yet.
The function should return the orders that Li Mei cannot start preparing before the end of her workday.
The time left in the shift will always be greater than 0. The array of juices to prepare will never be empty. Furthermore, the orders are prepared in the order in which they appear in the array. If Li Mei starts to mix a certain juice, she will always finish it even if she has to work a bit longer. If there are no remaining orders left that Dmitry needs to take care of, an empty vector should be returned.
julia> remaining_orders(5, ["Energizer", "All or Nothing", "Green Garden"])
["Green Garden"]
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