#ifndef TESTDUPLECATES_MAINWINDOW_HPP
#define TESTDUPLECATES_MAINWINDOW_HPP

#include <QtWidgets>

class CMainWindow: public QWidget
{
Q_OBJECT
public:
    CMainWindow(QWidget *parent = 0);
    ~CMainWindow();
private:
    QHBoxLayout *mainLayoutH;
    QHBoxLayout *buttonsLayoutH;
    QVBoxLayout *rightLayoutV;
    QVBoxLayout *displayLayout;

    QFrame      *leftFrame;
    QFrame      *rightFrame;
    QFrame      *bottonsFrame;

    QPushButton *buttonOpenFile;
    QPushButton *buttonFind;
    QPushButton *buttonSave;

    QTextEdit   *displayContentOfFile;
    QTextEdit   *infoAboutDup;

    void initWidgets();
    void initConnect();
private slots:
    void slotOpenFile();
    void slotFindDuplicates();
    void slotSaveInfo();
};
#endif //TESTDUPLECATES_MAINWINDOW_HPP

#include "CMainWindow.hpp"
CMainWindow::CMainWindow(QWidget *parent) : QWidget(parent)
{
    initWidgets();
    initConnect();
}

CMainWindow::~CMainWindow()
{

}

void CMainWindow::initWidgets()
{
    leftFrame = new QFrame();
    leftFrame->setLineWidth(1);
    leftFrame->setFixedSize(400, 500);
    rightFrame= new QFrame();
    rightFrame->setLineWidth(2);
    rightFrame->setFixedSize(300, 500);

    displayContentOfFile = new QTextEdit();
    displayContentOfFile->setReadOnly(true);

    displayLayout = new QVBoxLayout(leftFrame);
    displayLayout->setMargin(0);
    displayLayout->setSpacing(0);
    displayLayout->addWidget(displayContentOfFile);

    bottonsFrame = new QFrame();

    buttonOpenFile = new QPushButton("Open");
    buttonFind = new QPushButton("Find");
    buttonSave = new QPushButton("Save");

    buttonsLayoutH = new QHBoxLayout(bottonsFrame);
    buttonsLayoutH->addWidget(buttonOpenFile);
    buttonsLayoutH->addWidget(buttonFind);
    buttonsLayoutH->addWidget(buttonSave);

    infoAboutDup = new QTextEdit();
    infoAboutDup->setReadOnly(false);

    rightLayoutV = new QVBoxLayout(rightFrame);
    rightLayoutV->addWidget(bottonsFrame);
    rightLayoutV->addWidget(infoAboutDup);

    mainLayoutH = new QHBoxLayout(this);
    mainLayoutH->addWidget(leftFrame);
    mainLayoutH->addWidget(rightFrame);
    mainLayoutH->setMargin(0);
    mainLayoutH->setSpacing(0);
}
void CMainWindow::initConnect()
{
    connect(buttonOpenFile, SIGNAL(clicked()), this, SLOT(slotOpenFile()));
    connect(buttonFind, SIGNAL(clicked()), this, SLOT(slotFindDuplicates()));
    connect(buttonSave, SIGNAL(clicked()), this, SLOT(slotSaveInfo()));
}

void CMainWindow::slotOpenFile()
{
    QString file = QFileDialog::getOpenFileName(this, "Open File", "", "Text File(*.txt)");

    QFile f(file);
    if (!file.isEmpty())
    {
        if(!f.open(QIODevice::ReadOnly))
        {
            QMessageBox::critical(this, "Error", "Error opening file");
            return;
        }
        QString text = f.readAll();
        displayContentOfFile->setPlainText(text);
        f.close();
        qDebug() << file;
    }
}
void CMainWindow::slotFindDuplicates()
{

}
void CMainWindow::slotSaveInfo()
{
    QString filename = QFileDialog::getSaveFileName(this, "Save File", "", "*.txt");

    QFile f(filename);
    if (!filename.isEmpty())
    {
        if (!f.open(QIODevice::WriteOnly))
        {
            QMessageBox::critical(this, "Error", "Error writing text file!");
            return;
        }
        f.write(infoAboutDup->toPlainText().toLatin1());
        f.close();
        qDebug() << filename;
    }
}

#ifndef TESTDUPLECATES_MYDUPLICATES_HPP
#define TESTDUPLECATES_MYDUPLICATES_HPP

class MyDuplicates
{

};
#endif //TESTDUPLECATES_MYDUPLICATES_HPP

#include "MyDuplicates.hpp"

QStringList FindDuplicates(const QStringList& inputData) const

...
QString text = myTextEdit->text();  // myTextEdit - это ваш QTextEdit

QStringList splitText = text.split(",", QString::SkipEmptyParts);

QStringList duplicates = MyDuplicates::FindDuplicates(splitText);  // FindDuplicates - это и есть ваша функция из библиотеки

static QStringList FindDuplicates(const QStringList& inputData);