the following javaprogram decides whether two given lines in a twodimensional layer (defined by each two x- and y-coordinates) do cross or at least touch. precaution correct input (external input-method used). test it to crap.
import java.lang.Math;
class a0311b_cross {
public static void main (String[] args) {
double l1x1in,l1x2in,l1y1in,l1y2in,l2x1in,l2x2in,l2y1in,l2y2in,l1x1,l1x2,l1y1,l1y2,l2x1,l2x2,l2y1,l2y2,a,b,c,d,xs,ys;
boolean parallel, deckung, crossed;
int fall;
l1x1in = 0;
l1x2in = 0;
l1y1in = 0;
l1y2in = 0;
l2x1in = 0;
l2x2in = 0;
l2y1in = 0;
l2y2in = 0;
l1x1 = 0;
l1x2 = 0;
l1y1 = 0;
l1y2 = 0;
l2x1 = 0;
l2x2 = 0;
l2y1 = 0;
l2y2 = 0;
a = 0;
b = 0;
c = 0;
d = 0;
xs = 0;
ys = 0;
parallel = false;
deckung = false;
crossed = false;
fall = 0;
l1x1in = eingabe.readDouble ("Linie 1, x1:");
l1y1in = eingabe.readDouble ("Linie 1, y1:");
l1x2in = eingabe.readDouble ("Linie 1, x2:");
l1y2in = eingabe.readDouble ("Linie 1, y2:");
l2x1in = eingabe.readDouble ("Linie 2, x1:");
l2y1in = eingabe.readDouble ("Linie 2, y1:");
l2x2in = eingabe.readDouble ("Linie 2, x2:");
l2y2in = eingabe.readDouble ("Linie 2, y2:");
//l1, bottom to top
if ((l1x1in == l1x2in) && (l1y1in < l1y2in))
{
l1x1 = l1x1in;
l1x2 = l1x2in;
l1y1 = l1y1in;
l1y2 = l1y2in;
}
//l1, top to bottom
if ((l1x1in == l2x1in) && (l1y1in > l1y2in))
{
l1x1 = l1x2in;
l1y1 = l1y2in;
l1x2 = l1x1in;
l1y2 = l1y1in;
}
//l1, left to right
if ((l1x1in < l1x2in) && (l1y2in == l1y2in))
{
l1x1 = l1x1in;
l1x2 = l1x2in;
l1y1 = l1y1in;
l1y2 = l1y2in;
}
//l1, right to left
if ((l1x1in > l1x2in) && (l1y1in == l1y2in))
{
l1x1 = l1x2in;
l1y1 = l1y2in;
l1x2 = l1x1in;
l1y2 = l1y1in;
}
//l1, bottom left to top right
if ((l1x1in < l1x2in) && (l1y1in < l1y2in))
{
l1x1 = l1x1in;
l1x2 = l1x2in;
l1y1 = l1y1in;
l1y2 = l1y2in;
}
//l1, top right to bottom left
if ((l1x1in > l1x2in) && (l1y1in > l1y2in))
{
l1x1 = l1x2in;
l1y1 = l1y2in;
l1x2 = l1x1in;
l1y2 = l1y2in;
}
//l1, top left to bottom right
if ((l1x1in < l1x2in) && (l1y1in > l1y2in))
{
l1x1 = l1x1in;
l1x2 = l1x2in;
l1y1 = l1y1in;
l1y2 = l1y2in;
}
//l1, bottom right to top left
if ((l1x1in > l1x2in) && (l1y1in < l1y2in))
{
l1x1 = l1x2in;
l1y1 = l1y2in;
l1x2 = l1x1in;
l1y2 = l1y1in;
}
//l2, bottom to top
if ((l2x1in == l2x2in) && (l2y1in < l2y2in))
{
l2x1 = l2x1in;
l2x2 = l2x2in;
l2y1 = l2y1in;
l2y2 = l2y2in;
}
//l2, top to bottom
if ((l2x1in == l2x2in) && (l2y1in > l2y2in))
{
l2x1 = l2x2in;
l2y1 = l2y2in;
l2x2 = l2x1in;
l2y2 = l2y1in;
}
//l2, left to right
if (( l2x1in < l2x2in) && (l2y1in == l2y2in))
{
l2x1 = l2x1in;
l2x2 = l2x2in;
l2y1 = l2y1in;
l2y2 = l2y2in;
}
//l2, right to left
if ((l2x1in > l2x2in) && (l2y1in == l2y2in))
{
l2x1 = l2x2in;
l2y1 = l2y2in;
l2x2 = l2x1in;
l2y2 = l2y1in;
}
//l2, bottom left to top right
if ((l2x1in < l2x2in) && (l2y1in < l2y2in))
{
l2x1 = l2x1in;
l2x2 = l2x2in;
l2y1 = l2y1in;
l2y2 = l2y2in;
}
//l2, top right to bottom left
if ((l2x1in > l2x2in) && (l2y1in > l2y2in))
{
l2x1 = l2x2in;
l2y1 = l2y2in;
l2x2 = l2x1in;
l2y2 = l2y1in;
}
//l2, top left to bottom right
if ((l2x1in < l2x2in) && (l2y1in > l2y2in))
{
l2x1 = l2x1in;
l2x2 = l2x2in;
l2y1 = l2y1in;
l2y2 = l2y2in;
}
//l2, bottom right to top left
if ((l2x1in > l2x2in) && (l2y1in < l2y2in))
{
l2x1 = l2x2in;
l2y1 = l2y2in;
l2x2 = l2x1in;
l2y2 = l2y1in;
}
// | * | 1
if ((l1x1 == l1x2) && (l2x1 == l2x2)) { fall = 1; }
// | * - 2
else if ((l1x1 == l1x2) && (l2y1 == l2y2)) { fall = 2; }
// | * / 3
else if ((l1x1 == l1x2) && (l2y1 < l2y2)) { fall = 3; }
// | * \ 4
else if ((l1x1 == l1x2) && (l2y1 > l2y2)) { fall = 4; }
// - * | 5
else if ((l1y1 == l1y2) && (l2x1 == l2x2)) { fall = 5; }
// - * - 6
else if ((l1y1 == l1y2) && (l2y1 == l2y2)) { fall = 6; }
// - * / 7
else if ((l1y1 == l1y2) && (l2y1 < l2y2)) { fall = 7; }
// - * \ 8
else if ((l1y1 == l1y2) && (l2y1 > l2y2)) { fall = 8; }
// / * | 9
else if ((l1y1 < l1y2) && (l2x1 == l2x2)) { fall = 9; }
// / * - 10
else if ((l1y1 < l1y2) && (l2y1 == l2y2)) { fall = 10; }
// / * / 11
else if ((l1y1 < l1y2) && (l2y1 < l2y2)) { fall = 11; }
// / * \ 12
else if ((l1y1 < l1y2) && (l2y1 > l2y2)) { fall = 12; }
// \ * | 13
else if ((l1y1 > l1y2) && (l2x1 == l2x2)) { fall = 13; }
// \ * - 14
else if ((l1y1 > l1y2) && (l2y1 == l2y2)) { fall = 14; }
// \ * / 15
else if ((l1y1 > l1y2) && (l2y1 < l2y2)) { fall = 15; }
// \ * \ 16
else if ((l1y1 > l1y2) && (l2y1 > l2y2)) { fall = 16; }
switch (fall)
{
// hv * vh 1,2,5,6
case 1: case 2: case 5: case 6:
{
break;
}
// | * x 3,4
case 3: case 4:
{
c = (l2y2 - l2y1) / (l2x2 - l2x1);
d = l2y1 - (c * l2x1);
xs = l1x1;
ys = (c * xs) + d;
break;
}
// x * | 9,13
case 9: case 13:
{
a = (l1y2 - l1y1) / (l1x2 - l1x1);
b = l1y1 - (a * l1x1);
xs = l2x1;
ys = (a * xs) + b;
break;
}
case 7: case 8: case 10: case 11: case 12: case 14: case 15: case 16:
{
a = (l1y2 - l1y1) / (l1x2 - l1x1);
c = (l2y2 - l2y1) / (l2x2 - l2x1);
b = l1y1 - (a * l1x1);
d = l2y1 - (c * l2x1);
if (a == c)
{
if (b == d)
{ deckung = true; }
else { deckung = false;
parallel = true; }
}
else { xs = (d - b) / (a - c); }
ys = (a * xs) + b;
break;
}
default:
{
//cannot be reached
break;
}
}
switch (fall)
{
// | * | 1
case 1:
{
if ((l1x1 == l2x1) && (((l2y1 >= l1y1) && (l2y1 <= l1y2)) || ((l2y2 >= l1y1) && (l2y2 <= l1y2))))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// | * - 2
case 2:
{
if (((l2y1 >= l1y1) && (l2y1 <= l1y2)) && ((l1x1 >= l2x1) && (l1x1 <= l2x2)))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// - * | 5
case 5:
{
if (((l2x1 >= l1x1) && (l2x1 <= l1x2)) && ((l1y1 >= l2y1) && (l1y1 <= l2y2)))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// - * - 6
case 6:
{
if ((l1y1 == l2y1) && (((l2x1 >= l1x1) && (l2x1 <= l1x2)) || ((l2x2 >= l1x1) && (l2x2 <= l1x2))))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// | * / 3, | * \ 4
case 3: case 4:
{
if ((ys >= l1y1) && (ys <= l1y1))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// / * | 9, \ * | 13
case 9: case 13:
{
if ((ys >= l2y1) && (ys <= l2y2))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// up-up
case 10: case 7: case 11:
{
if (parallel) { crossed = false; }
else if (deckung)
{
if (((l2x1 >= l1x1) && (l2x1 <= l1x2)) || ((l2x2 >= l1x1) && (l2x2 <= l1x2)))
{ crossed = true; }
else { crossed = false; }
}
else
{
if ((((xs >= l1x1) && (xs <= l1x2)) && ((ys >= l1y1) && (ys <= l1y2))) &&
(((xs >= l2x1) && (xs <= l2x2)) && ((ys >= l2y1) && (ys <= l2y2))))
{ crossed = true; }
else
{ crossed = false; }
}
break;
}
// up-down
case 12:
{
if ((((xs >= l1x1) && (xs <= l1x2)) && ((ys >= l1y1) && (ys <= l1y2))) &&
(((xs >= l2x1) && (xs <= l2x2)) && ((ys <= l2y1) && (ys >= l2y2))))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// down-up
case 15:
{
if ((((xs >= l1x1) && (xs <= l1x2)) && ((ys <= l1y2) && (ys >= l1y2))) &&
(((xs >= l2x1) && (xs <= l2x2)) && ((ys >= l2y1) && (ys <= l2y2))))
{ crossed = true; }
else
{ crossed = false; }
break;
}
// down-down
case 16: case 14: case 8:
{
if (parallel) { crossed = false; }
else if (deckung)
{
if (((l2x1 >= l1x1) && (l2x1 <= l1x2)) || ((l2x2 >= l1x1) && (l2x2 <= l1x2)))
{ crossed = true; }
else { crossed = false; }
}
else
{
if ((((xs <= l1x1) && (xs >= l1x2)) && ((ys <= l1y1) && (ys >= l1y2))) &&
(((xs <= l2x1) && (xs >= l2x2)) && ((ys <= l2y1) && (ys >= l2y2))))
{ crossed = true; }
else { crossed = false; }
}
break;
}
//zero
default:
{
//cannot be reached
break;
}
}
if (crossed)
{
System.out.println ("the lines do cross or at least touch");
}
else
{
System.out.println ("the lines neither cross nor touch");
}
}
}
