Implementation of a Trie In Swift Sample

SwiftTrie.swift

// Description: Implementation of a Trie
//
// Language: Swift 2.1
// Author: Paul Ossenbruggen
// Nov 7, 2015

import Foundation

class Trie  {
    var last : Bool = false
    var children : Dictionary<Character, Trie> = [:]

    init(last : Bool) {
        self.last = last
    }
    
    static func addWords(words : [String]) -> Trie {
        let root =  Trie(last: false)
        for word in words {
            print(word)
            root.addRemaining(word.lowercaseString)
        }
        return root
    }
    
    func addRemaining(var word : String) {
        let char = word.removeAtIndex(word.startIndex)
        var child = children[char]
        if child == nil {
            child = Trie(last: word.isEmpty)
            children[char] = child
        }
        if !word.isEmpty {
            child!.addRemaining(word)
        }
    }
    
    func findBase(var word  : String) -> Trie? {
        if !word.isEmpty {
            let char = word.removeAtIndex(word.startIndex)
            if let trie = children[char] {
                return trie.findBase(word)
            }
        }
        return self
    }
    
//    var description : String {
//        return "Trie \(last) \(children)"
//    }
    
    func compileResultsFromBase(var baseString: String, inout results : [String])  {
        if last {
            results.append(baseString)
        }
        
        for (key, value) in children {
            baseString.append(key)
            value.compileResultsFromBase(baseString, results: &results)
        }
    }
    
    func findValuesForTerm(string : String) -> [String] {
        let base = findBase(string)
        var results = [String]()
        base?.compileResultsFromBase(string, results: &results)
        return results
    }
}

// findall the words under that starting prefix
func findAllWords(term : String) -> [String]? {
    do {
        // just read the first 100 words from dictionary.
        let file = try String(contentsOfFile: "/usr/share/dict/words", encoding: NSUTF8StringEncoding)
        let words  = Array(file.componentsSeparatedByString("\n")[0..<100])
        words.count
        let root = Trie.addWords(words)
        let results = root.findValuesForTerm(term)
        return results
    } catch {
        print("error")
    }
    return nil
}
// see reults in Playground
findAllWords("ab")
findAllWords("aa")