リストの数字を最大になるように並べる

NumGen.swift

#!/usr/bin/env xcrun swift

func NumGen(numList: [Int]) -> String {
    var strList = [String]()
    var str = ""
    for var i = 0;  i < numList.count; i++ {
        strList.append( String(numList[i]) )
    }
    strList.sort { $1 < $0 }
    for var i = 0;  i < strList.count; i++ {
        str = str + strList[i]
    }
    return str
}

var numList = [15,12,13,5]
var str:String = ""
str = NumGen(numList)
println(str)