第六章第三十九題(幾何学:点の位置)(Geometry:point position)-プログラミング練習問題の答え

6.39(ジオメトリ:点の位置)プログラミング練習問題3.32は、点が直線の左側、右側、またはその直線上にあるかどうかをテストする方法を示します.次のメソッドヘッダを使用して、メソッドを記述します.
public static boolean leftOfTheLine(double x0, double y0, double x1, double y1, double x2, double y2)
public static boolean onTheSameLine(double x0, double y0, double x1, double y1, double x2, double y2)
public static boolean onTheLineSegment(double x0, double y0, double x1, double y1, double x2, double y2)
p 0、p 1、p 2に3つの点を入力して、p 0からp 1までの直線の左側、右側、直線上、または線分上にあるかどうかを示すプログラムを作成する.
次の例を示します.
Enter three points for p0, p1, and p2: 1 1 2 2 1.5 1.5
(1.5, 1.5) is on the line segment from (1.0, 1.0) to (2.0, 2.0)
Enter three points for p0, p1, and p2: 1 1 2 2 3 3
(3.0, 3.0) is on the same line from (1.0, 1.0) to (2.0, 2.0)
Enter three points for p0, p1, and p2: 1 1 2 2 1 1.5
(1.0, 1.5) is on the left side of the line from (1.0, 1.0) to (2.0, 2.0)
Enter three points for p0, p1, and p2: 1 1 2 2 1 –1
(1.0, −1.0) is on the right side of the line from (1.0, 1.0) to (2.0, 2.0)
6.39(Geometry: point position) Programming Exercise 3.32 shows how to test whether a point is on the left side of a directed line, on the right, or on the same line. Write the methods with the following headers:
public static boolean leftOfTheLine(double x0, double y0, double x1, double y1, double x2, double y2)
public static boolean onTheSameLine(double x0, double y0, double x1, double y1, double x2, double y2)
public static boolean onTheLineSegment(double x0, double y0, double x1, double y1, double x2, double y2)
Write a program that prompts the user to enter the three points for p0, p1, and p2and displays whether p2 is on the left side of the line from p0 to p1, right side, the same line, or on the line segment.
Here are some sample runs:
Enter three points for p0, p1, and p2: 1 1 2 2 1.5 1.5
(1.5, 1.5) is on the line segment from (1.0, 1.0) to (2.0, 2.0)
Enter three points for p0, p1, and p2: 1 1 2 2 3 3
(3.0, 3.0) is on the same line from (1.0, 1.0) to (2.0, 2.0)
Enter three points for p0, p1, and p2: 1 1 2 2 1 1.5
(1.0, 1.5) is on the left side of the line from (1.0, 1.0) to (2.0, 2.0)
Enter three points for p0, p1, and p2: 1 1 2 2 1 –1
(1.0, −1.0) is on the right side of the line from (1.0, 1.0) to (2.0, 2.0)
次は、参考答案コードです.

// https://cn.fankuiba.com
import java.util.Scanner;

public class Ans6_39_page205 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter three points for p0, p1, and p2:");
        double x0 = input.nextDouble();
        double y0 = input.nextDouble();
        double x1 = input.nextDouble();
        double y1 = input.nextDouble();
        double x2 = input.nextDouble();
        double y2 = input.nextDouble();

        if (onTheSameLine(x0, y0, x1, y1, x2, y2)) {
            if (onTheLineSegment(x0, y0, x1, y1, x2, y2)) {
                System.out.printf("(%.1f, %.1f) is on the line segment from "
                        + "(%.1f, %.1f) to (%.1f, %.1f)", x2, y2, x0, y0, x1, y1);
            } else {
                System.out.printf("(%.1f, %.1f) is on the same line from "
                        + "(%.1f, %.1f) to (%.1f, %.1f)", x2, y2, x0, y0, x1, y1);
            }
        } else {
            if (leftOfTheLine(x0, y0, x1, y1, x2, y2)) {
                System.out.printf("(%.1f, %.1f) is on the left side of the line from "
                        + "(%.1f, %.1f) to (%.1f, %.1f)", x2, y2, x0, y0, x1, y1);
            } else {
                System.out.printf("(%.1f, %.1f) is on the right side of the line from "
                        + "(%.1f, %.1f) to (%.1f, %.1f)", x2, y2, x0, y0, x1, y1);
            }
        }
    }

    public static boolean leftOfTheLine(double x0, double y0,
                                        double x1, double y1, double x2, double y2) {
        if ((x1 - x0) * (y2 - y0) - (x2 - x0) * (y1 - y0) > 0)
            return true;
        else
            return false;
    }

    public static boolean onTheSameLine(double x0, double y0,
                                        double x1, double y1, double x2, double y2) {
        return (x1 - x0) * (y2 - y0) - (x2 - x0) * (y1 - y0) == 0;
    }

    public static boolean onTheLineSegment(double x0, double y0,
                                           double x1, double y1, double x2, double y2) {
        if ((x1 - x0) * (y2 - y0) - (x2 - x0) * (y1 - y0) == 0 &&
                x2 <= (Math.max(x0, x1)) && x2 >= (Math.min(x1, x0)))
            return true;
        else
            return false;
    }
}

適用Java言語プログラミングとデータ構造(基礎編)(原書第11版)Java言語プログラミング(基礎編)(原書第10/11版)
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