the trie data structure write in swift

Trie.swift

import Foundation


"use xcode's playground"

/**
* port as3 to swift
* http://www.anotherearlymorning.com/2009/06/trie-data-structure-in-actionscript-3/
* http://www.emanueleferonato.com/2009/07/13/trie-data-structure-in-actionscript-3/
*
*/
class Trie
{
    private var letters = [Character:TrieData]()
    
    func get(jumble:String)->[String]
    {
        var result:[String] = []
        var s:Character = jumble[advance(jumble.startIndex, 0)]
        if let d = letters[s] {
            getRecursivelyFor(jumble, charIndex: 1, withData: d, result: &result)
        }
        return result
    }
    
    func add(word:String)
    {
        var s = word[advance(word.startIndex, 0)]
        var d = letters[s]
        if d == nil {
            d = TrieData()
            letters[s] = d
        }
        addRecursivelyFor(word, charIndex: 1, withData: d!)
    }
    
    private func addRecursivelyFor(word:String, var charIndex:Int, withData:TrieData)
    {
        var len = countElements(word)
        if charIndex == len {
            return
        }
        var s:Character = word[advance(word.startIndex, charIndex)]
        var d = withData.children[s]
        if d == nil {
            d = TrieData()
            withData.children[s] = d
        }
        if charIndex == len - 1 {
            d!.isWord = true
        }
        else{
            addRecursivelyFor(word, charIndex: ++charIndex, withData: d!)
        }
    }
    
    private func getRecursivelyFor(word:String, var charIndex:Int, withData:TrieData, inout result:[String])
    {
        var count = countElements(word)
        if count == charIndex {
            return
        }
        var s:Character = word[advance(word.startIndex, charIndex)]
        if let c = withData.children[s]{
            if c.isWord {
                var findWord = word.substringWithRange(Range<String.Index>(start:advance(word.startIndex, 0),
                    end:advance(word.startIndex, charIndex + 1)))
                result.append(findWord)
            }
            getRecursivelyFor(word, charIndex:++charIndex, withData: c, result: &result)
        }
    }
}

class TrieData
{
    var isWord = false
    var children = [Character:TrieData]()
}

//example
var trie = Trie();
trie.add("program");
trie.add("programming");

var result = trie.get("programming");
println(result); //[program, programming]

1.在swift中数组是数值类型, 是传值的, 所以在方法的声明中, 使用了inout修饰符, 也可以不使用, 修改完直接return回给调用方
2.类方法的第二个参数开始默认都有一个external name, 在调用时需要填写。
3.字符串截取所需参数不是Int 类型的, 而是String.Index类型, advance为全局函数。
4.swift中除了字符串类型, 还有字符类型。对于单个字符的字面值, swift推导类型默认为String, 所以如果需要字符型, 需要自己指定。
5.使用optional binding将optional内部值存储至某变量。