Title:
A convex polygon with four vertices is divided into four triangles, as shown.
Write a program that prompts the user to enter the coordinates of four vertices, and then displays the area of the four triangles in ascending order.
源代码如下：
package com;
import java.util.Scanner;
public class test {
public static void main(String[] args) {
System.out.println(“Enter x1, y1, x2, y2, x3, y3, x4, y4:”);
double[][] points = new double[4][2];
Scanner in = new Scanner(System.in);
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 2; j++) {
points[i][j] = in.nextDouble();
}
}
double array[]=getIntersectingPoint(points);
System.out.print(“Intersecting point: (”);
for(int i=0;i<2;i++) {
if (i == 1) {
System.out.print(array[i] + ") ");
} else {
System.out.print(array[i] + “,”);
}
}
double x=array[0];
double y=array[1];
double x1 = points[0][0];
double y1 = points[0][1];
double x2 = points[1][0];
double y2 = points[1][1];
double x3 = points[2][0];
double y3 = points[2][1];
double x4 = points[3][0];
double y4 = points[3][1];
double[] S=new double[4];
S[0]= Math.abs((x1y2+x2y+xy1-x1y-x2y1-xy2)/2);
S[1]=Math.abs((x1y4+x4y+xy1-x1y-x4y1-xy4)/2);
S[2]=Math.abs((x3y2+x2y+xy3-x3y-x2y3-xy2)/2);
S[3]=Math.abs((x3y4+x4y+xy3-x3y-x4y3-xy4)/2);
bubble(S);
System.out.println();
System.out.print("The areas are ");
for(int i=0;i<4;i++) {
if (i == 3) {
System.out.print(S[i]);
} else {
System.out.print(S[i] + " ");
}
}
}
public static double[] getIntersectingPoint(double[][] points){
double x1 = points[0][0];
double y1 = points[0][1];
double x2 = points[1][0];
double y2 = points[1][1];
double x3 = points[2][0];
double y3 = points[2][1];
double x4 = points[3][0];
double y4 = points[3][1];
double K1 = (y1-y3)/ (x1-x3);
double K2 = (y2-y4)/ (x2-x4);
double[] arr=new double[2];
double B1 = y1 - K1x1 ;
double B2 = y2 - K2x2 ;
arr[0]= (B2 - B1) / (K1 - K2);
arr[1]= (B2 * K1 - B1 * K2) / (K1 - K2);
return arr;
}
public static void bubble(double[] S){
double temp;
for(int i = 0; i<S.length; i++){
for (int j = S.length-1; j > i; j–) {
if (S[j] < S[j - 1]) {
temp = S[j - 1];
S[j - 1] = S[j];
S[j] = temp;
}
}
}
}
}
Knowledge about the intersection of this question can be seen on my previous blog.
The main final area ascending algorithm indicates that bubble sorting is used, which is relatively simple and basic.
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