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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	public static void main (String[] args) throws java.lang.Exception
  11. 	{
  12. 		Scanner in = new Scanner( System.in);
  13.     double p1x, p1y, p2x, p2y; //point
  14.     double x, y; //intersection points
  15.     double cx, cy, r; //circle
  16.  
  17.     System.out.print("Enter cx: ");
  18.     cx = in.nextDouble();
  19.     System.out.print("Enter cy: ");
  20.     cy = in.nextDouble();
  21.     System.out.print("Enter r: ");
  22.     r = in.nextDouble();
  23.     System.out.print("Enter p1x: ");
  24.     p1x = in.nextDouble();
  25.     System.out.print("Enter p1y: ");
  26.     p1y = in.nextDouble();
  27.     System.out.print("Enter p2x: ");
  28.     p2x = in.nextDouble();
  29.     System.out.print("Enter p2y: ");
  30.     p2y = in.nextDouble();
  31.  
  32.     if(p2x == p1x){
  33.     	//line is vertical, or both points are in the same position.
  34.     	double dx = p2x - cx;
  35.     	if(dx*dx<r*r){
  36.     		//infinite line hits circle check y values.
  37.  
  38.     	} else{
  39.     		System.out.println("doesn't touch.");
  40.     	}
  41.     } else{
  42.  
  43.         double m = (p2y - p1y)/(p2x - p1x);
  44.  
  45.         double b = p1y - m*p1x;
  46.  
  47.         double B = (b - m*cx-cy);
  48.         if((r*r*(m*m+1))>B*B){
  49.     	    //inifinite line hits the circle. Now to solve the actual x positions.
  50.     	    double radical = Math.sqrt((m*m+1)*r*r - B*B);
  51.     	    double x0 = cx + (-m*B + radical)/(m*m+1);
  52.     	    double x1 = cx + (-m*B - radical)/(m*m+1);
  53.     	    System.out.println("infinite line touches at: " + x0 + ", and " + x1);
  54.             //finaly check if either x0 or x1 are between p1x and p2x.
  55.             if((x0>p1x&&x0<p2x)||(x0>p2x&&x0<p1x)||(x1>p1x&&x1<p2x)||(x1>p2x&&x1<p1x)){
  56.             	System.out.println("line segment touches");
  57.             }
  58.         } else{
  59.     	    System.out.println("doesn't touch");
  60.         }
  61.     }
  62. 	}
  63. }
Success #stdin #stdout 0.06s 711680KB
comments (?)
stdin 
1.0 1.0 3.0 0.0 0.0 8.0 10.0
stdout 
Enter cx: Enter cy: Enter r: Enter p1x: Enter p1y: Enter p2x: Enter p2y: infinite line touches at: 3.75322563399777, and 0.4418963172217425
line segment touches
https://ideone.com/DjE8eR
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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