Иллюстрация быстрой сортировки

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include <QTimer>
#include <QVector>
#include <random>
 
#include "canvas.h"
 
namespace Ui {
class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private slots:
    void on_pushButton_start_clicked();
    void on_tmr();
 
private:
    Ui::MainWindow *ui;
    std::default_random_engine generator;
    QVector<int> arr;
    int ii;
    QTimer tmr;
};
 
#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
 
#include <chrono>
#include <algorithm>
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    generator(std::chrono::system_clock::now().time_since_epoch().count())
{
    ui->setupUi(this);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::on_pushButton_start_clicked()
{
    std::uniform_int_distribution<int> d(ui->spinBox_min->value(), ui->spinBox_max->value());
    arr.resize(ui->spinBox_count->value());
    for (int &i : arr) i = d(generator);
    ii = 0;
    connect(&tmr, SIGNAL(timeout()), this, SLOT(on_tmr()));
    tmr.start(250);
    ui->pushButton_start->setEnabled(false);
}
 
void MainWindow::on_tmr()
{
    for (int i = ii; i < arr.size(); ++i)
    {
        int min = i;
        for (int j = i + 1; j < arr.size(); ++j)
            if (arr[j] < arr[min])
                min = j;
 
        if (min != i)
        {
            std::swap(arr[i], arr[min]);
            ui->widget_canvas->Draw(arr);
            ii = i + 1;
            return;
        }
    }
    disconnect(&tmr, SIGNAL(timeout()), this, SLOT(on_tmr()));
    tmr.stop();
    ui->pushButton_start->setEnabled(true);
}

#ifndef CANVAS_H
#define CANVAS_H
 
#include <QWidget>
 
class Canvas : public QWidget
{
    Q_OBJECT
public:
    explicit Canvas(QWidget *parent = 0);
 
signals:
 
public slots:
    void Draw(QVector<int> a);
 
protected:
    void paintEvent(QPaintEvent *event);
    QVector<int> arr;
};
 
#endif // CANVAS_H

#include "canvas.h"
 
#include <QPainter>
 
Canvas::Canvas(QWidget *parent) : QWidget(parent)
{
}
 
void Canvas::Draw(QVector<int> a)
{
    arr = a;
    update();
}
 
void Canvas::paintEvent(QPaintEvent *event)
{
    QPainter painter;
    painter.begin(this);
 
    for (int i = 0; i < arr.size(); ++i)
        if (i % 2 == 0) painter.fillRect(15 * i, height() - 15 * arr[i], 15, 15 * arr[i], Qt::GlobalColor::blue);
        else painter.fillRect(15 * i, height() - 15 * arr[i], 15, 15 * arr[i], QColor(255, 170, 0));
 
    painter.setPen(QColor(0, 85, 0));
    for (int i = 0; i < height(); i += 15)
        painter.drawLine(0, height() - i, width(), height() - i);
    for (int i = 0; i < width(); i += 15)
        painter.drawLine(i, 0, i, width());
 
    painter.end();
}