hangman constraint issue

class ViewController: UIViewController {

    // letterGuess
    // usedLetters
    // score/lives

    var scoreLabel: UILabel!
    var answerLabel: UILabel!
    var characterButtons = [UIButton]()

    let width:CGFloat = 100
    let height:CGFloat = 100

    var score = 0 {
        didSet {
            scoreLabel.text = "Score: \(score)"
        }
    }
    override func loadView() {
        view = UIView()
        view.backgroundColor = .white

        scoreLabel = UILabel()
        scoreLabel.translatesAutoresizingMaskIntoConstraints = false
        scoreLabel.textAlignment = .right
        scoreLabel.font = UIFont.systemFont(ofSize: 24)
        scoreLabel.text = "Score: 0"
        view.addSubview(scoreLabel)

        answerLabel = UILabel()
        answerLabel.translatesAutoresizingMaskIntoConstraints = false
        answerLabel.font = UIFont.systemFont(ofSize: 24)
        answerLabel.text = "ANSWER"
        answerLabel.numberOfLines = 1
        answerLabel.textAlignment = .center
        answerLabel.setContentHuggingPriority(UILayoutPriority(1), for: .vertical)
        view.addSubview(answerLabel)

        let buttonsView = UIView()
        buttonsView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(buttonsView)

        let row1View = UIView()
        row1View.clipsToBounds = true
        row1View.translatesAutoresizingMaskIntoConstraints = false
        buttonsView.addSubview(row1View)

        let row2View = UIView()
        row2View.clipsToBounds = true

        row2View.translatesAutoresizingMaskIntoConstraints = false
        row2View.setContentHuggingPriority(.defaultLow, for: .vertical)
        buttonsView.addSubview(row2View)

        let row3View = UIView()
        row3View.clipsToBounds = true

        row3View.translatesAutoresizingMaskIntoConstraints = false
        buttonsView.addSubview(row3View)


        NSLayoutConstraint.activate([
            scoreLabel.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor),
            scoreLabel.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: 0),

            answerLabel.topAnchor.constraint(equalTo: scoreLabel.bottomAnchor, constant: 25),
            answerLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),

            buttonsView.widthAnchor.constraint(equalToConstant: 1000),
            buttonsView.heightAnchor.constraint(equalToConstant: 300),
            buttonsView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            buttonsView.topAnchor.constraint(equalTo: answerLabel.bottomAnchor, constant: 20),
            buttonsView.bottomAnchor.constraint(equalTo: view.layoutMarginsGuide.bottomAnchor, constant: -20),

            row1View.leftAnchor.constraint(equalTo: buttonsView.leftAnchor),
            row1View.topAnchor.constraint(equalTo: buttonsView.topAnchor),
            row1View.widthAnchor.constraint(equalTo: buttonsView.widthAnchor),
            row1View.heightAnchor.constraint(equalToConstant: height),

            row2View.leftAnchor.constraint(equalTo: buttonsView.leftAnchor),
            row2View.topAnchor.constraint(equalTo: row1View.bottomAnchor),
            row2View.widthAnchor.constraint(equalTo: buttonsView.widthAnchor),
            row2View.heightAnchor.constraint(equalToConstant: height),

            row3View.leftAnchor.constraint(equalTo: buttonsView.leftAnchor),
            row3View.topAnchor.constraint(equalTo: row2View.bottomAnchor),
            row3View.widthAnchor.constraint(equalTo: buttonsView.widthAnchor),
            row3View.heightAnchor.constraint(equalToConstant: height)


        ])


        var i = 10

        for row in 0..<3 {
            print(row)
            switch row {
            case 0:
                i = 10
            case 1:
                i = 9
            case 2:
                i = 7
            default:
                return
            }
            for col in 0..<i {
                let characterButton = UIButton(type: .system)
                characterButton.titleLabel?.font = UIFont.systemFont(ofSize: 36)

                characterButton.layer.borderWidth = 1
                characterButton.layer.borderColor = UIColor.lightGray.cgColor
                characterButton.layer.backgroundColor = UIColor.white.cgColor
                characterButton.setTitle("#", for: .normal)

                let frame = CGRect(x: CGFloat(col) * width, y: 0, width: width, height: height)
                characterButton.frame = frame

                switch row {
                case 0:
                    print(row)
                    print("row 1")
                    row1View.addSubview(characterButton)
                case 1:
                    print(row)
                    print("row 2")
                    row2View.addSubview(characterButton)
                case 2:
                    print(row)
                    print("row 3")
                    row3View.addSubview(characterButton)
                default:
                    print("defualt")
                    return
                }

                characterButton.addTarget(self, action: #selector(buttonFunction), for: .touchUpInside)
            }
        }

        buttonsView.backgroundColor = .purple
        row1View.backgroundColor = .red
        row2View.backgroundColor = .yellow
        row3View.backgroundColor = .green

    }

    @objc func buttonFunction(){
        //your code goes here
    }

}