01 Snippet

# Source URL: https://dev.epicgames.com/community/snippets/N04/fortnite-random-permutation-picker-device
# Local doc:  epic-docs/community/snippets/N04/fortnite-random-permutation-picker-device.md
  using { /Fortnite.com/Devices }
  using { /Verse.org/Random }
  using { /Verse.org/Simulation }
  using { /UnrealEngine.com/Temporary/Diagnostics }
  # The random_permutation_picker device generates a random permutation of
  # its Choices and then picks them one at a time, without item repetition, with Pick.
  # When the last choice has been picked, a new permutation is generated.
  random_permutation_picker_device := class(creative_device):
  @editable
  PickButton:button_device = button_device{}
  # The Choices array is the set of elements to be picked.
  @editable
  var<private> Choices:[]switch_device = array{}
  var<private> PickStartIndex<private>:int=0
  # Pick one of the Choices, without repetition.
  # The algorithm uses a form of the Fisher-Yates shuffle to generate a random permutation.
  # See https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
  # for a description of the Fisher-Yates shuffle algorithm.
  Pick<public>()<transacts><decides>:switch_device=
  # Imagine a hat with all the Choices in it.
  # The hat is full at the start of the permutation.
  # PickStartIndex is the index of the first element in the hat.
  # We pick an element from the hat, remove it from the hat, and return it.
  # When the hat is empty, we refill it and start a new permutation.
  # Generate a random integer between PickStartIndex and Choices.Length-1, inclusive.
  # This is the index of the element to be picked.
  PickedIndex := GetRandomInt(PickStartIndex, Choices.Length-1)
  # Select the element at PickedIndex. We'll swap it with the element at PickStartIndex and return it.