我已经在这几个小时,尝试不同的方法看几乎每个问题。也许我完全错了,但我觉得我的数学是正确的,但无论我输入什么数字,我都得到相同的输出。我的代码在某个地方关闭,我必须在午夜之前将其打开。
这一切都很有趣:找出一个点是否在三角形代码中。 (适合初学者)
import java.util.Scanner;
public class PointsTriangle {
// checks if point entered is within the triangle
//given points of triangle are (0,0) (0,100) (200,0)
public static void main (String [] args) {
//obtain point (x,y) from user
System.out.print("Enter a point's x- and y-coordinates: ");
Scanner input = new Scanner(System.in);
double x = input.nextDouble();
double y = input.nextDouble();
//find area of triangle with given points
double ABC = ((0*(100-0 )+0*(0 -0)+200*(0-100))/2.0);
double PAB = ((x*(0 -100)+0*(100-y)+0 *(y- 0))/2.0);
double PBC = ((x*(100-0 )+0*(0 -y)+200*(y-100))/2.0);
double PAC = ((x*(0 -100)+0*(100-y)+200*(y- 0))/2.0);
boolean isInTriangle = PAB + PBC + PAC == ABC;
if (isInTriangle)
System.out.println("The point is in the triangle");
else
System.out.println("The point is not in the triangle");
}//end main
}//end PointsTriangle
答案 0 :(得分:5)
如果您绘制图片,您可以看到该点必须满足简单的不等式(某些线的右下方/上方/右侧)。无论“处于边缘”是否进入,我都会留给你:
Y > 0 (above the X axis)
X > 0 (to the right of the Y axis)
X + 2* Y < 200 (below the hypotenuse)
围绕这三个写一个if语句,你就完成了:
if( (y > 0) && (x > 0) && (x + 2*y < 200) )
System.out.println("The point is in the triangle");
else
System.out.println("The point is not in the triangle");
答案 1 :(得分:5)
您将错误的值顺序放入公式中;因此,结果是错误的。如果3个顶点如下
A(x1, y1) B(x2, y2), C(x3, y3)
然后该区域计算为
double ABC = Math.abs (x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2;
之后,你只需用输入点替换每个顶点,我们将有以下三角形:PBC,APC,ABP。
把所有东西放在一起,我们会有正确的
int x1 = 0, y1 = 0;
int x2 = 0, y2 = 100;
int x3 = 200, y3 = 0;
// no need to divide by 2.0 here, since it is not necessary in the equation
double ABC = Math.abs (x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2));
double ABP = Math.abs (x1 * (y2 - y) + x2 * (y - y1) + x * (y1 - y2));
double APC = Math.abs (x1 * (y - y3) + x * (y3 - y1) + x3 * (y1 - y));
double PBC = Math.abs (x * (y2 - y3) + x2 * (y3 - y) + x3 * (y - y2));
boolean isInTriangle = ABP + APC + PBC == ABC;