【Swift】2つの配列を交互につなぎ合わせる ref: http://qiita.com/ken0nek/items/55e9ac0be32d35fbaa67

file0.swift

let num = 1234

// Int -> [String]
let numList = String(num).characters.flatMap { String($0) }
print(numList)
// ["1", "2", "3", "4"]

let opeList = ["+", "-", "*"]
let zipped = zip(numList, opeList + [""]) // 要素数を合わせる
print(zipped)
// Zip2Sequence<Array<String>, Array<String>>(_sequence1: ["1", "2", "3", "4"], _sequence2: ["+", "-", "*", ""])

let equation = zipped.reduce("") { $0 + $1.0 + $1.1 }
print(equation)
// "1+2-3*4"

file1.swift

let num = 1234

// Int -> [String]
let numList = String(num).characters.flatMap { String($0) }
print(numList)
// ["1", "2", "3", "4"]

let opeList = ["+", "-", "*"]
let zipped = zip(numList, opeList + [""])
print(zipped)
// Zip2Sequence<Array<String>, Array<String>>(_sequence1: ["1", "2", "3", "4"], _sequence2: ["+", "-", "*", ""])

let concatenated = zipped.map { $0.0 + $0.1 }
print(concatenated)
// ["1+", "2-", "3*", "4"]

let equation = concatenated.joined()
print(equation)
// "1+2-3*4"

file2.swift

let num = 1234

// Int -> [String]
let numList = String(num).characters.flatMap { String($0) }
print(numList)
// ["1", "2", "3", "4"]

let opeList = ["+", "-", "*"]
let zipped = zip(numList, opeList + [""]) // 要素数を合わせる
print(zipped)
// Zip2Sequence<Array<String>, Array<String>>(_sequences: (["1", "2", "3", "4"], ["+", "-", "*", ""]))

let equation = zipped.reduce("") { $0 + $1.0 + $1.1 }
print(equation)
// "1+2-3*4"

file3.swift

let num = 1234

// Int -> [String]
let numList = String(num).characters.flatMap { String($0) }
print(numList)
// ["1", "2", "3", "4"]

let opeList = ["+", "-", "*"]
let zipped = zip(numList, opeList + [""])
print(zipped)
// Zip2Sequence<Array<String>, Array<String>>(_sequences: (["1", "2", "3", "4"], ["+", "-", "*", ""]))

let concatenated = zipped.map { $0.0 + $0.1 }
print(concatenated)
// ["1+", "2-", "3*", "4"]

let equation = "".join(concatenated)
print(equation)
// "1+2-3*4"

map-join

let num = 1234

// Int -> [String]
let numList = String(num).characters.flatMap { String($0) }
print(numList)
// ["1", "2", "3", "4"]

let opeList = ["+", "-", "*"]
let zipped = zip(numList, opeList + [""])
print(zipped)
// Zip2Sequence<Array<String>, Array<String>>(_sequences: (["1", "2", "3", "4"], ["+", "-", "*", ""]))

let concatenated = zipped.map { $0.0 + $0.1 }
print(concatenated)
// ["1+", "2-", "3*", "4"]

let equation = "".join(concatenated)
print(equation)
// "1+2-3*4"

reduce

let num = 1234

// Int -> [String]
let numList = String(num).characters.flatMap { String($0) }
print(numList)
// ["1", "2", "3", "4"]

let opeList = ["+", "-", "*"]
let zipped = zip(numList, opeList + [""]) // 要素数を合わせる
print(zipped)
// Zip2Sequence<Array<String>, Array<String>>(_sequences: (["1", "2", "3", "4"], ["+", "-", "*", ""]))

let equation = zipped.reduce("") { $0 + $1.0 + $1.1 }
print(equation)
// "1+2-3*4"