Task: Sierpinski curve


C++: 
#include <cmath>
#include <fstream>
#include <iostream>
#include <string>

class sierpinski_curve {
public:
    void write(std::ostream& out, int size, int length, int order);
private:
    static std::string rewrite(const std::string& s);
    void line(std::ostream& out);
    void execute(std::ostream& out, const std::string& s);
    double x_;
    double y_;
    int angle_;
    int length_;
};

void sierpinski_curve::write(std::ostream& out, int size, int length, int order) {
    length_ = length;
    x_ = length/std::sqrt(2.0);
    y_ = 2 * x_;
    angle_ = 45;
    out << "<svg xmlns='http:
        << size << "' height='" << size << "'>\n";
    out << "<rect width='100%' height='100%' fill='white'/>\n";
    out << "<path stroke-width='1' stroke='black' fill='none' d='";
    std::string s = "F--XF--F--XF";
    for (int i = 0; i < order; ++i)
        s = rewrite(s);
    execute(out, s);
    out << "'/>\n</svg>\n";
}

std::string sierpinski_curve::rewrite(const std::string& s) {
    std::string t;
    for (char c : s) {
        if (c == 'X')
            t += "XF+G+XF--F--XF+G+X";
        else
            t += c;
    }
    return t;
}

void sierpinski_curve::line(std::ostream& out) {
    double theta = (3.14159265359 * angle_)/180.0;
    x_ += length_ * std::cos(theta);
    y_ -= length_ * std::sin(theta);
    out << " L" << x_ << ',' << y_;
}

void sierpinski_curve::execute(std::ostream& out, const std::string& s) {
    out << 'M' << x_ << ',' << y_;
    for (char c : s) {
        switch (c) {
        case 'F':
        case 'G':
            line(out);
            break;
        case '+':
            angle_ = (angle_ + 45) % 360;
            break;
        case '-':
            angle_ = (angle_ - 45) % 360;
            break;
        }
    }
}

int main() {
    std::ofstream out("sierpinski_curve.svg");
    if (!out) {
        std::cerr << "Cannot open output file\n";
        return 1;
    }
    sierpinski_curve s;
    s.write(out, 545, 7, 5);
    return 0;
}




Java: import java.io.*;

public class SierpinskiCurve {
    public static void main(final String[] args) {
        try (Writer writer = new BufferedWriter(new FileWriter("sierpinski_curve.svg"))) {
            SierpinskiCurve s = new SierpinskiCurve(writer);
            s.currentAngle = 45;
            s.currentX = 5;
            s.currentY = 10;
            s.lineLength = 7;
            s.begin(545);
            s.execute(rewrite(5));
            s.end();
        } catch (final Exception ex) {
            ex.printStackTrace();
        }
    }

    private SierpinskiCurve(final Writer writer) {
        this.writer = writer;
    }

    private void begin(final int size) throws IOException {
        write("<svg xmlns='http:
        write("<rect width='100%%' height='100%%' fill='white'/>\n");
        write("<path stroke-width='1' stroke='black' fill='none' d='");
    }

    private void end() throws IOException {
        write("'/>\n</svg>\n");
    }

    private void execute(final String s) throws IOException {
        write("M%g,%g\n", currentX, currentY);
        for (int i = 0, n = s.length(); i < n; ++i) {
            switch (s.charAt(i)) {
                case 'F':
                case 'G':
                    line(lineLength);
                    break;
                case '+':
                    turn(ANGLE);
                    break;
                case '-':
                    turn(-ANGLE);
                    break;
            }
        }
    }

    private void line(final double length) throws IOException {
        final double theta = (Math.PI * currentAngle) / 180.0;
        currentX += length * Math.cos(theta);
        currentY -= length * Math.sin(theta);
        write("L%g,%g\n", currentX, currentY);
    }

    private void turn(final int angle) {
        currentAngle = (currentAngle + angle) % 360;
    }

    private void write(final String format, final Object... args) throws IOException {
        writer.write(String.format(format, args));
    }

    private static String rewrite(final int order) {
        String s = AXIOM;
        for (int i = 0; i < order; ++i) {
            final StringBuilder sb = new StringBuilder();
            for (int j = 0, n = s.length(); j < n; ++j) {
                final char ch = s.charAt(j);
                if (ch == 'X')
                    sb.append(PRODUCTION);
                else
                    sb.append(ch);
            }
            s = sb.toString();
        }
        return s;
    }

    private final Writer writer;
    private double lineLength;
    private double currentX;
    private double currentY;
    private int currentAngle;

    private static final String AXIOM = "F--XF--F--XF";
    private static final String PRODUCTION = "XF+G+XF--F--XF+G+X";
    private static final int ANGLE = 45;
}