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copied!<p>Your calculations seem quite long, and I do not see the use of the different cases you test. Anyway, since I found the problem interesting I attempted to solve it myself and came up with the following. Feel free to replace <code>double radius</code> by <code>int radius</code> and use <code>IntPoint</code>s, but be aware that every time you cast, as discussed in the comments, results that are not exact integer intersection points will become wrong.</p> <p>The background of the calculations performed is this: From point A, a scaled version of vector AB points to a point on the circle. That point has distance radius from center. Hence, |AC + scalingFactor * AB|=r.</p> <pre><code>import java.util.Arrays; import java.util.Collections; import java.util.List; public class CircleLine { public static List<Point> getCircleLineIntersectionPoint(Point pointA, Point pointB, Point center, double radius) { double baX = pointB.x - pointA.x; double baY = pointB.y - pointA.y; double caX = center.x - pointA.x; double caY = center.y - pointA.y; double a = baX * baX + baY * baY; double bBy2 = baX * caX + baY * caY; double c = caX * caX + caY * caY - radius * radius; double pBy2 = bBy2 / a; double q = c / a; double disc = pBy2 * pBy2 - q; if (disc < 0) { return Collections.emptyList(); } // if disc == 0 ... dealt with later double tmpSqrt = Math.sqrt(disc); double abScalingFactor1 = -pBy2 + tmpSqrt; double abScalingFactor2 = -pBy2 - tmpSqrt; Point p1 = new Point(pointA.x - baX * abScalingFactor1, pointA.y - baY * abScalingFactor1); if (disc == 0) { // abScalingFactor1 == abScalingFactor2 return Collections.singletonList(p1); } Point p2 = new Point(pointA.x - baX * abScalingFactor2, pointA.y - baY * abScalingFactor2); return Arrays.asList(p1, p2); } static class Point { double x, y; public Point(double x, double y) { this.x = x; this.y = y; } @Override public String toString() { return "Point [x=" + x + ", y=" + y + "]"; } } public static void main(String[] args) { System.out.println(getCircleLineIntersectionPoint(new Point(-3, -3), new Point(-3, 3), new Point(0, 0), 5)); System.out.println(getCircleLineIntersectionPoint(new Point(0, -2), new Point(1, -2), new Point(1, 1), 5)); System.out.println(getCircleLineIntersectionPoint(new Point(1, -1), new Point(-1, 0), new Point(-1, 1), 5)); System.out.println(getCircleLineIntersectionPoint(new Point(-3, -3), new Point(-2, -2), new Point(0, 0), Math.sqrt(2))); } </code></pre>

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