Exercism/julia/annalyns-infiltration

Annalyns Infiltration

Welcome to Annalyns Infiltration on Exercism’s Julia Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Booleans in Julia

True or false values are represented by the Bool type. It contains only two values: true and false.

julia> true
true

julia> false
false

Boolean Operators

There are three Boolean operators in Julia.

&& is Boolean “and”. It evaluates to true if the expressions on both sides of && are true.

julia> true && true
true

julia> true && false
false

|| is Boolean “or”. It evaluates to true if an expression on either side of || is true.

julia> true || true
true

julia> false || true
true

! is Boolean “not”. It exchanges true and false values.

julia> !true
false

julia> !false
true

For longer and more complicated expressions, it is best to use parentheses to make your intention clear.

julia> (true || false) && (false && true)
false

Instructions

In this exercise, you’ll be writing some logic for a video game a friend is developing. The game’s main character is Annalyn, a brave girl with a fierce and loyal pet dog. Unfortunately, disaster strikes, as her best friend is kidnapped while searching for berries in the forest. Annalyn will try to find and free her friend, optionally taking her dog with her on this quest.

Annalyn eventually finds the camp in which her friend is imprisoned and it turns out there are two kidnappers: a mighty knight and a cunning archer.

The player is presented with some options for what to do next. For each of the four possible options you need to write a function that tells the game whether it should show that option or not.

1. Check if the ‘Fast Attack’ option should be shown

If the knight is sleeping, then Annalyn will be able to make a quick attack into the camp before he can wake up properly and get his armour on.

Implement a function named can_do_fast_attack that takes a boolean value which indicates if the knight is awake. This function returns true if the ‘Fast Attack’ action is available based on the state of the character. Otherwise, returns false:

julia> knight_awake = true

julia> can_do_fast_attack(knight_awake)
false

2. Check if the ‘Spy’ option should be shown

The group can be spied upon if at least one of them is awake. Otherwise, spying is a waste of time.

Implement a function named can_spy that takes three boolean values, indicating if the knight, archer and prisoner, respectively, are awake. The function returns true if the ‘Spy’ action is available based on the state of the characters. Otherwise, returns false:

# Output suppressed from the next 3 lines
julia> knight_awake = false
julia> archer_awake = true
julia> prisoner_awake = false

julia> can_spy(knight_awake, archer_awake, prisoner_awake)
true

3. Check if the ‘Signal Prisoner’ option should be shown

The prisoner can be signalled using bird sounds if she is awake and the archer is sleeping. If the archer is awake then she can’t be safely signaled because the archer is also trained in bird signalling.

Implement a function named can_signal_prisoner that takes two boolean values, indicating if the archer and prisoner, respectively, are awake. The function returns true if the ‘Signal Prisoner’ action is available based on the state of the characters. Otherwise, returns false:

julia> archer_awake = false
julia> prisoner_awake = true

julia> can_signal_prisoner(archer_awake, prisoner_awake)
true

4. Check if the ‘Free Prisoner’ option should be shown

Annalyn can try sneaking into the camp to free her friend. This is a risky thing to do and can only succeed in one of two ways:

• If Annalyn has her pet dog with her, she can rescue the prisoner if the archer is asleep. The knight is scared of the dog and the archer will not have time to get ready before Annalyn and her friend can escape.

• If Annalyn does not have her dog then she and the prisoner must be very sneaky! Annalyn can free the prisoner if she is awake and the knight and archer are both sleeping, but if the prisoner is sleeping, she can’t be rescued: she would be startled by Annalyn’s sudden appearance and wake up the knight and archer.

Implement a function named can_free_prisoner that takes four boolean values. The first three parameters indicate if the knight, archer and prisoner, respectively, are awake. The last parameter indicates if Annalyn’s pet dog is present. The function returns true if the ‘Free Prisoner’ action is available based on the state of the characters. Otherwise, it returns false:

julia> knight_awake = false
julia> archer_awake = true
julia> prisoner_awake = false
julia> dog_present = false

julia> can_free_prisoner(knight_awake, archer_awake, prisoner_awake, dog_present)
false

Source

Created by

• @SaschaMann
• @colinleach

Contributed to by

• @cmcaine
• @BNAndras