【Swift】2つの配列から辞書を作る ref: http://qiita.com/ken0nek/items/8e97692eeaeda6eb5770

file0.swift

let romanStrs = ["M", "D", "C", "L", "X", "V", "I"]
let romanNums = [1000, 500, 100, 50, 10, 5, 1]

let romanToNum = zip(romanStrs, romanNums).reduce([String: Int]()) { (dic, t) in
    var dic = dic
    dic[t.1] = t.0
    return dic
}

print(romanToNum)
// ["X": 10, "V": 5, "D": 500, "C": 100, "L": 50, "I": 1, "M": 1000]