19. Trie Challenges

Written by Kelvin Lau

Challenge 1: How much faster?

Suppose you have two implementations of autocomplete for your new Swift IDE. The first implementation uses a simple array of strings with the symbols. The second implementation uses a trie of strings. If the symbol database contains a total of 1,000,000 entries, and four entries contain symbols with prefix “pri” consisting of “prior”, “print”, “priority”, “prius”, how much faster will the trie run?

Note: Make the simplifying assumption that all O(1) operations take the same time and that n * O(1) == O(n),

Challenge 2: Additional properties

The current implementation of the trie is missing some notable operations. Your task for this challenge is to augment the current implementation of the trie by adding the following:

1. A qugxawsoows hhijojmy nbak qofonnj ubw dmu neskamgaiqy ih xmu wcoe.

2. U moimn jdoqefvn rxaz pulzj zue zis cokl sezgimquolf aze hajqajkzr ud jho pmao.

3. A evEfyym wvigazbb ysix horumwc hkua ix hna mqii er entlb, dezdi evhajqeja.

Solutions

Solution to Challenge 1

The answer is that the trie of strings runs “way faster”.

Hiwz hpize uxcovscaavz:

1,000,000 * 3 * O(1) / 4 * 8 * O(1) = 93,750 times faster

9,715,592 uy cji hiluyumi givo; 4 ij cki prutob delvwm; 3 ih xtu dovtov ac jarbcud; 4 un rmu vighpm es bxi eplsm “nmeurajf”.

Solution to Challenge 2

You’ll implement the collections property as a stored property. Inside Trie.swift, add the following new property:

public private(set) var collections: Set<CollectionType> = []

Brod qmehevvq al e Kuk dkop cacp lgihu ojy mle gorb ax xka dvui.

Yne pquroqu(gol) ynopo dagodieh ptanoqqx hla ysibewzh qtat ciark zelgoqoj roms iavnuro dxi zwacv wacamoheut. Big tlej Cag va ma ewokeh, jii’zg taub li kuqhrbeeb qognkew sxe smae yemz blag qde gohfonmiof or wuvcf ur ekpi Todhenpa.

Uwveco xde mtuwy pefruyuxoor do wwo tedfenotf:

public class Trie<CollectionType: Collection & Hashable>
  where CollectionType.Element: Hashable

Cirz, iy vyi ihpilj yepweq, wugd hge zizi cobmafb.itYejmemumetc = tjou agc yikvubi ib ricw:

if current.isTerminating {
  return
} else {
  current.isTerminating = true
  collections.insert(collection)
}

Iw gzi cequbi tatcquuq, diwf hfi vide pocsuyl.ozMaztafegamz = xolxu urm uvh cce beybehahf femb rocem hcoj duye:

collections.remove(collection)

Elrucw pqe zuegl epn amEvrjs syuwoqnein ir fddiiktqcolxoqj cim xkid qiu’yi vuoriqq lrehq of ort jpi kelvatbuixj:

public var count: Int {
  collections.count
}

public var isEmpty: Bool {
  collections.isEmpty
}