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65 lines
2.7 KiB
Java
65 lines
2.7 KiB
Java
import java.awt.geom.*;
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import java.util.Random;
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public class SegmentsIntersection {
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public static boolean isCrossIntersect(long x1, long y1, long x2, long y2, long x3, long y3, long x4, long y4) {
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long z1 = (x2 - x1) * (y3 - y1) - (y2 - y1) * (x3 - x1);
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long z2 = (x2 - x1) * (y4 - y1) - (y2 - y1) * (x4 - x1);
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long z3 = (x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3);
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long z4 = (x4 - x3) * (y2 - y3) - (y4 - y3) * (x2 - x3);
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return (z1 < 0 || z2 < 0) && (z1 > 0 || z2 > 0) && (z3 < 0 || z4 < 0) && (z3 > 0 || z4 > 0);
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}
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public static boolean isCrossOrTouchIntersect(long x1, long y1, long x2, long y2, long x3, long y3, long x4, long y4) {
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if (Math.max(x1, x2) < Math.min(x3, x4) || Math.max(x3, x4) < Math.min(x1, x2)
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|| Math.max(y1, y2) < Math.min(y3, y4) || Math.max(y3, y4) < Math.min(y1, y2))
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return false;
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long z1 = (x2 - x1) * (y3 - y1) - (y2 - y1) * (x3 - x1);
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long z2 = (x2 - x1) * (y4 - y1) - (y2 - y1) * (x4 - x1);
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long z3 = (x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3);
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long z4 = (x4 - x3) * (y2 - y3) - (y4 - y3) * (x2 - x3);
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return (z1 <= 0 || z2 <= 0) && (z1 >= 0 || z2 >= 0) && (z3 <= 0 || z4 <= 0) && (z3 >= 0 || z4 >= 0);
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}
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public static Point2D.Double getLinesIntersection(long x1, long y1, long x2, long y2, long x3, long y3, long x4, long y4) {
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long a1 = y2 - y1;
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long b1 = x1 - x2;
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long c1 = -(x1 * y2 - x2 * y1);
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long a2 = y4 - y3;
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long b2 = x3 - x4;
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long c2 = -(x3 * y4 - x4 * y3);
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long det = a1 * b2 - a2 * b1;
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if (det == 0)
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return null;
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double x = -(c1 * b2 - c2 * b1) / (double) det;
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double y = -(a1 * c2 - a2 * c1) / (double) det;
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return new Point2D.Double(x, y);
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}
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// random tests
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public static void main(String[] args) {
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Random rnd = new Random();
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for (int step = 0; step < 1000_000; step++) {
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int r = 10;
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int x1 = rnd.nextInt(r) - r / 2;
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int y1 = rnd.nextInt(r) - r / 2;
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int x2 = rnd.nextInt(r) - r / 2;
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int y2 = rnd.nextInt(r) - r / 2;
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int x3 = rnd.nextInt(r) - r / 2;
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int y3 = rnd.nextInt(r) - r / 2;
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int x4 = rnd.nextInt(r) - r / 2;
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int y4 = rnd.nextInt(r) - r / 2;
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boolean crossIntersect = isCrossIntersect(x1, y1, x2, y2, x3, y3, x4, y4);
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boolean crossOrTouchIntersect = isCrossOrTouchIntersect(x1, y1, x2, y2, x3, y3, x4, y4);
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boolean crossOrTouchIntersect2 = Line2D.linesIntersect(x1, y1, x2, y2, x3, y3, x4, y4);
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crossOrTouchIntersect2 &= !(x1 == x2 && y1 == y2 && x3 == x4 && y3 == y4 && (x1 != x3 || y1 != y3)); // applying fix
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if (crossOrTouchIntersect != crossOrTouchIntersect2 || crossIntersect && !crossOrTouchIntersect)
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throw new RuntimeException();
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}
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System.out.println(getLinesIntersection(0, 0, 4, 2, 2, -1, 2, 5).equals(new Point2D.Double(2, 1)));
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}
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}
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