Xcode Swift Functional Programming alternative and Unit Test for InterviewCake stock price question. ⚠️ For the full experience, join https://interviewcake.com and visit https://www.interviewcake.com/question/swift/stock-price

InterviewCake-StockPrice.swift

//
//  InterviewCake-StockPrice.swift
//
//  Copyright © 2018 Xavier Schott
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import Foundation

class StockPrice {
    func getMaxProfit(from stockPrices:[Int]) -> Int {

        var minPrice = Int.max
        var maxProfit = Int.min

        stockPrices.forEach { (currentPrice) in
            maxProfit = max(maxProfit, currentPrice - minPrice)
            minPrice = min(minPrice, currentPrice)
        }

        return maxProfit
    }
}

InterviewCake-StockPricesTests.swift

//
//  StockPriceTests.swift
//
//  Copyright © 2018 Xavier Schott
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import XCTest

class appleStockPriceTests: XCTestCase {
    func testGetMaxProfit() {
        let result = StockPrice().getMaxProfit(from: [12, 7, 5, 8, 11, 9, 1, 5])
        XCTAssertTrue(6 == result)
    }

    func testGetMaxProfitGoingDownAllDay() {
        let result = StockPrice().getMaxProfit(from: [100, 90, 79, 67, 54, 40, 25, 9])
        XCTAssertTrue(-10 == result)
    }

    func testGetMaxProfitSingleRise() {
        let result = StockPrice().getMaxProfit(from: [100, 90, 80, 70, 80, 50, 40, 30, 20, 10])
        XCTAssertTrue(10 == result)
    }

    func testGetMaxProfitZeroEntry() {
        // Not designed to return meaningful value with less than 2 entries
        let result = StockPrice().getMaxProfit(from: [])
        XCTAssertTrue(Int.min == result)
    }

    func testGetMaxProfitOneEntry() {
        // Not designed to return meaningful value with less than 2 entries
        let result = StockPrice().getMaxProfit(from: [20])
        XCTAssertTrue(Int.min + 20 + 1 == result)
    }
}