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Swift Algorithm Club: Hash Tables

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1

Learn how to implement a hash table data structure in Swift, in this step-by-step tutorial from the Swift Algorithm Club.

This is a companion discussion topic for the original entry at https://www.raywenderlich.com/206-swift-algorithm-club-hash-tables
2

Hi, Kelvin.

Thanks for the article, great explanation of what is the essence of HashTable.

I found a small type in your code:

public func value(for key: Key) -> Value? {
  let index = self.index(for: key)
  return buckets[index].first { $0.key == key }?.value
}

There should be filter instead of first.

3

You’re welcome!

Could you elaborate on why filter would work better? filter returns an array of elements matching the closure logic, and first is essentially a filter that stops when it finds the first match.

4

Sorry, my bad!

I didn’t know that an array has first API method.

5

Hi Kelvin,
i Am particularly interested in this function

func djb2Hash(_ string: String) → Int {
let unicodeScalars = string.unicodeScalars.map { $0.value }
return unicodeScalars.reduce(5381) {
($0 << 5) &+ $0 &+ Int($1)
}
}

I am calling djb@Hash(“a”)
so here $0 = 5381 and $1 = 97 (unicode value of “a”)

My question is how we are getting the value $1 inside the .reduce?

6

reduce takes a closure with two parameters. $0 references the first parameter, while $1 references the second parameter.

In this context, $1 refers a particular character of the String during a particular iterative step.

9

This tutorial is more than six months old so questions are no longer supported at the moment for it. Thank you!