using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace c_equation
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if ((string.IsNullOrEmpty(textBox1.Text)) || (string.IsNullOrEmpty(textBox2.Text)) || (string.IsNullOrEmpty(textBox3.Text)) || (string.IsNullOrEmpty(textBox4.Text)))
            {
                MessageBox.Show("数値を入力してください。");
                return;
            }

            double a = Convert.ToDouble(textBox1.Text);
            double b = Convert.ToDouble(textBox2.Text);
            double c = Convert.ToDouble(textBox3.Text);
            double d = Convert.ToDouble(textBox4.Text);
            double x1, x2, x3 = 0.0;

            int result = kai(a, b, c, d, out x1, out x2, out x3);

            if (result == 0)
            {
                textBox5.Text = x1.ToString();
                textBox6.Text = "重解";
                textBox7.Text = "重解";
            }
            else if (result == 1)
            {
                if (x1 == x2)
                {
                    x1 = x3;
                    x3 = x2;
                }
                if (x1 == x3)
                {
                    x1 = x2;
                    x2 = x3;
                }
                textBox5.Text = x1.ToString();
                textBox6.Text = x2.ToString();
                textBox7.Text = "重解";
            }
            else if (result == 2)
            {
                textBox5.Text = x1.ToString();
                textBox6.Text = "複素数解";
                textBox7.Text = "複素数解";
            }
            else if (result == 3)
            {
                textBox5.Text = x1.ToString();
                textBox6.Text = x2.ToString();
                textBox7.Text = x3.ToString();
            }
            else if (result == 4)
            {
                textBox5.Text = x2.ToString();
                textBox6.Text = x3.ToString();
                textBox7.Text = "";
            }
            else if (result == -1)
            {
                textBox5.Text = "複素数解";
                textBox6.Text = "";
                textBox7.Text = "";
            }
            else if (result == -2)
            {
                textBox5.Text = "";
                textBox6.Text = x2.ToString();
                textBox7.Text = "重解";
            }
            else if (result == -3)
            {
                textBox5.Text = x1.ToString();
                textBox6.Text = "";
                textBox7.Text = "";
            }
            else if (result == -4)
            {
                textBox5.Text = "不能";
                textBox6.Text = "";
                textBox7.Text = "";
            }
            else if (result == -5)
            {
                textBox5.Text = "不定";
                textBox6.Text = "";
                textBox7.Text = "";
            }
        }

        private int kai(double a, double b, double c, double d, out double x1, out double x2, out double x3)
        {
            x1 = x2 = x3 = 0.0;

            if ((a == 0.0) && (b == 0.0) && (c == 0.0) && (d == 0.0))
            {
                return -5;
            }
            else if ((a == 0.0) && (b == 0.0) && (c == 0.0))
            {
                return -4;
            }
            else if ((a == 0.0) && (b == 0.0))
            {
                x1 = -c / d;
                return -3;
            }
            else if (a == 0.0)
            {
                int result = q_equation(b, c, d, out x2, out x3);
                return result;
            }

            double hanbetu = -4.0 * a * (c * c * c) - 27.0 * (a * a) * (d * d) -
                4.0 * (b * b * b) * d + (b * b) * (c * c) + (18.0 * a * b * c * d);

            bool x_hantei = true;
            double sanji = 0.0;
            double x = 1.0;
            double[] nijihan1 = new double[4] { a, b, c, d };
            double[] nijihan2 = new double[2];

                if (hanbetu > 0.0)
                {
                    while (x_hantei)
                    {
                        if (a == 1.0)
                        {
                            sanji = (a * (x * x * x)) + (b * (x * x)) + (c * x) + d;

                            if (sanji == 0.0)
                            {
                                x1 = a = x;
                                nijihan2[0] = 1.0;
                                nijihan2[1] = -(a);
                                x_hantei = false;
                            }
                        }
                        else if (a > 1.0)
                        {
                            x1 = 1.0 / a;
                            nijihan2[0] = a;
                            nijihan2[1] = -(1.0);
                            x_hantei = false;
                        }

                        x = -(x);
                        if (x > 0)
                        {
                            x++;
                        }
                    }
                    nijiOut(nijihan1, nijihan2, out a, out b, out c);
                    int result = q_equation(a, b, c, out x2, out x3);
                    return 3;
                }
                else if (hanbetu < 0.0)
                {
                    while (x_hantei)
                    {
                        sanji = (a * (x * x * x)) + (b * (x * x)) + (c * x) + d;
                        if (sanji == 0.0)
                        {
                            x1 = x;
                            return 2;
                        }
                        x = -(x);
                        if (x > 0)
                        {
                            x++;
                        }
                    }
                }
                else if (hanbetu == 0.0)
                {
                    double hanbetu2 = (-2 * (b * b * b)) + (9 * a * b * c) - (27 * d * (a * a));
                    if (hanbetu2 == 0)
                    {
                        return 0;
                    }
                    else
                    {
                        nijihan2[0] = x1 = a;
                        nijihan2[1] = -(x);
                        x1 = x;
                        nijiOut(nijihan1, nijihan2, out a, out b, out c);
                        int result = q_equation(a, b, c, out x2, out x3);
                        return 1;
                    }
                }
            return 1;
        }

        private void nijiOut(double[] nijihan1, double[] nijihan2, out double a, out double b, out double c)
        {
            double[] niji = new double[3];

            for (int i = 0; i < 3; i++)
            {
                double y = nijihan1[i] / nijihan2[0];
                nijihan1[i] = nijihan1[i] - (y * nijihan2[0]);
                nijihan1[i + 1] = nijihan1[i + 1] - (y * nijihan2[1]);
                niji[i] = y;
            }
            a = niji[0];
            b = niji[1];
            c = niji[2];
        }

        private int q_equation(double a, double b, double c, out double x2, out double x3)
        {
            x2 = x3 = 0.0;

            double root = b * b - 4.0 * a * c;

            if (Math.Abs(root) < 0.000001)
            {
                x2 = x3 = (-b) / (2.0 * a);
                return -2;
            }
            else if (root < 0.0)
            {
                return -1;
            }
            else
            {
                x2 = (-b - Math.Sqrt(root)) / (2.0 * a);
                x3 = (-b + Math.Sqrt(root)) / (2.0 * a);
                return 4;
            }
        }
    }
}