Изменить цвет фона для выделенной динамической ячейки Tableview Swift 4

Question

Я создаю вопросы и ответы с множественным выбором, используя Tableview.Я изменил вопросы в зависимости от выбора ответа, а также у меня есть кнопка Prev, чтобы пользователь мог изменить ответ на предыдущий вопрос.Мне нужно изменить цвет выбранной ячейки ответа таблицы просмотра.Я пытаюсь изменить цвет в методе didselect row, но когда я нажимаю кнопку prev, цвет не меняется, как этого добиться

//  ViewController.swift
//  QuestionarY
//
//  Created by Muthupalaniappan S on 20/09/19.
//  Copyright © 2019 Sensiple. All rights reserved.
//

import UIKit

struct Question {
    var questionString: String?
    var answers: [String]?
    var selectedAnswerIndex: Int?
}

var questionsList: [Question] = [Question(questionString: "What is your favorite type of food?", answers: ["Sandwiches", "Pizza", "Seafood", "Unagi"], selectedAnswerIndex: nil), Question(questionString: "What do you do for a living?", answers: ["Paleontologist", "Actor", "Chef", "Waitress"], selectedAnswerIndex: nil), Question(questionString: "Were you on a break?", answers: ["Yes", "No"], selectedAnswerIndex: nil)]

class QuestionController: UITableViewController {

    let cellId = "cellId"
    let headerId = "headerId"

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.title = "Question"

        navigationController?.navigationBar.tintColor = .white
        navigationItem.backBarButtonItem = UIBarButtonItem(title: "Back", style: .plain, target: nil, action: nil)

        tableView.register(AnswerCell.self, forCellReuseIdentifier: cellId)
        tableView.register(QuestionHeader.self, forHeaderFooterViewReuseIdentifier: headerId)

        tableView.sectionHeaderHeight = 50
        tableView.tableFooterView = UIView()
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {


        if let index = navigationController?.viewControllers.firstIndex(of: self) {
            let question = questionsList[index]
            if let count = question.answers?.count {
                return count
            }
        }
        return 0
    }
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath) as! AnswerCell

        if let index = navigationController?.viewControllers.firstIndex(of: self) {
            let question = questionsList[index]
            cell.nameLabel.text = question.answers?[indexPath.row]
        }

        return cell
    }



    override func  tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {

        let header = tableView.dequeueReusableHeaderFooterView(withIdentifier: headerId) as! QuestionHeader

        if let index = navigationController?.viewControllers.firstIndex(of: self) {
            let question = questionsList[index]
            header.nameLabel.text = question.questionString
        }

        return header
    }

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

        if let index = navigationController?.viewControllers.firstIndex(of: self) {
            questionsList[index].selectedAnswerIndex = indexPath.item

            if index < questionsList.count - 1 {
                let questionController = QuestionController()
                navigationController?.pushViewController(questionController, animated: true)
            } else {
                let controller = ResultsController()
                navigationController?.pushViewController(controller, animated: true)
            }
        }
    }

}

class ResultsController: UIViewController {

    let resultsLabel: UILabel = {
        let label = UILabel()
        label.text = "Congratulations, you're a total Ross!"
        label.translatesAutoresizingMaskIntoConstraints = false
        label.textAlignment = .center
        label.font = UIFont.boldSystemFont(ofSize: 14)
        return label
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Done", style: .plain, target: self, action: #selector(done))

        navigationItem.title = "Results"

        view.backgroundColor = .white

        view.addSubview(resultsLabel)
        view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[v0]|", options: NSLayoutConstraint.FormatOptions(), metrics: nil, views: ["v0": resultsLabel]))
        view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[v0]|", options: NSLayoutConstraint.FormatOptions(), metrics: nil, views: ["v0": resultsLabel]))

        let names = ["Ross", "Joey", "Chandler", "Monica", "Rachel", "Phoebe"]

        var score = 0
        for question in questionsList {
            score += question.selectedAnswerIndex!
        }

        let result = names[score % names.count]
        resultsLabel.text = "Congratulations, you're a total \(result)!"
    }

    @objc func done() {
        navigationController?.popToRootViewController(animated: true)
    }

}

class QuestionHeader: UITableViewHeaderFooterView {

    override init(reuseIdentifier: String?) {
        super.init(reuseIdentifier: reuseIdentifier)
        setupViews()
    }

    let nameLabel: UILabel = {
        let label = UILabel()
        label.text = "Sample Question"
        label.font = UIFont.boldSystemFont(ofSize: 14)
        label.translatesAutoresizingMaskIntoConstraints = false
        return label
    }()

    func setupViews() {
        addSubview(nameLabel)
        addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-16-[v0]|", options: NSLayoutConstraint.FormatOptions(), metrics: nil, views: ["v0": nameLabel]))
        addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[v0]|", options: NSLayoutConstraint.FormatOptions(), metrics: nil, views: ["v0": nameLabel]))
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

class AnswerCell: UITableViewCell {

    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        setupViews()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    let nameLabel: UILabel = {
        let label = UILabel()
        label.text = "Sample Answer"
        label.font = UIFont.systemFont(ofSize: 16)
        label.translatesAutoresizingMaskIntoConstraints = false
        return label
    }()

    func setupViews() {
        addSubview(nameLabel)
        addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-16-[v0]|", options: NSLayoutConstraint.FormatOptions(), metrics: nil, views: ["v0": nameLabel]))
        addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[v0]|", options: NSLayoutConstraint.FormatOptions(), metrics: nil, views: ["v0": nameLabel]))
    }

}