MainWindow.cpp

#include <QTime>
#include <QtMath>

#include "MainWindow.h"
#include "ui_MainWindow.h"

MainWindow::MainWindow(QWidget *parent)
	: QMainWindow(parent)
	, ui(new Ui::MainWindow)
{
	ui->setupUi(this);
}

MainWindow::~MainWindow()
{
	delete ui;
}

#include <iostream>
void MainWindow::on_lineEditNumber_textEdited(const QString &arg1)
{
//    std::cout << qPrintable(arg1) << std::endl;
    bool enable = arg1.trimmed().length() > 0;
    this->ui->pushButtonCalculate->setEnabled(enable);
}

void MainWindow::on_pushButtonStop_clicked()
{
    this->userStopped = true;
}

void MainWindow::on_pushButtonCalculate_clicked()
{
    bool isValid = true;
    const QString& text = this->ui->lineEditNumber->text();

    long long int number = text.toLongLong(&isValid);

    if ( isValid )
    {
        this->ui->plainTextEditResults->clear();
        this->ui->pushButtonCalculate->setEnabled(false);
        this->ui->pushButtonStop->setEnabled(true);
        this->userStopped = false;
        ui->statusBar->showMessage( tr("Calculating...") );

        QTime time;
        time.start();
        long long sumCount = this->calculate(number);
        double seconds = time.elapsed() / 1000.0;

        this->ui->pushButtonCalculate->setEnabled(true);
        this->ui->pushButtonStop->setEnabled(false);
        ui->statusBar->showMessage( tr("%1 sums found in %2 seconds").arg(sumCount).arg(seconds) );
    }
    else
    {
        ui->statusBar->showMessage( tr("Invalid number: %1").arg(text) );
    }
}


long long MainWindow::calculate(long long number)
{
    if ( number < 4 || number == 5 ) return 0;
    return number % 2 == 0 ? calculateEvenGoldbach(number) : calculateOddGoldbach(number);
}

long long MainWindow::calculateEvenGoldbach(long long number)
{
    long long results = 0;
    for ( long long a = 2; a < number && this->userStopped == false; ++a )
    {
        if ( ! isPrime(a) ) continue;
        long long b = number - a;
        if ( b >= a && isPrime(b) )
            this->ui->plainTextEditResults->appendPlainText( tr("%1: %2 + %3").arg(++results).arg(a).arg(b) );
    }
    return results;
}

long long MainWindow::calculateOddGoldbach(long long number)
{
    long long results = 0;
    for ( long long a = 2; a < number; ++a )
    {
        if ( ! isPrime(a) ) continue;
        for ( long long b = a; b < number; ++b )
        {
            if ( this->userStopped )
                return results;

            if ( ! isPrime(b) ) continue;
            long long c = number - a - b;
            if ( c >= b && isPrime(c) )
                this->ui->plainTextEditResults->appendPlainText( tr("%1: %2 + %3 + %4").arg(++results).arg(a).arg(b).arg(c) );
        }
    }
    return results;
}

bool MainWindow::isPrime(long long number)
{
    if ( number < 2 ) return false;

    long long last = static_cast<long long>( qSqrt( number) );
    for ( long long i = 2; i <= last; ++i )
        if ( number % i == 0 )
            return false;

    return true;
}