customComp.swift

struct I : Comparable {
    let v: Int
    static func <(lhs: I, rhs: I) -> Bool { return lhs.v < rhs.v }
    static func ==(lhs: I, rhs: I) -> Bool { return lhs.v == rhs.v }
}

let source = repeatElement(1...1000, count: 1000).joined().map(I.init)
let n = 3

func foo() -> Int {
    var checksum = 0
    if CommandLine.arguments.first == "by" {
        for _ in 1...n {
          let sorted = source.sorted(by: <)
          checksum += sorted.first!.v
        }
    } else {
        for _ in 1...n {
          let sorted = source.sorted()
          checksum += sorted.first!.v
        }
    }
    return checksum
}
print(foo())