AOJ Volume0 no.012
no10をちょっと、応用した問題。解法はほぼ同じ。
package levelZero; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; class APointinaTriangle { /** * @param args * @throws IOException */ public static void main(String[] args) throws IOException { triangle(); } private static void triangle() throws IOException { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); String buf = br.readLine(); String[] triangle = buf.split(" "); double x1 = Double.parseDouble(triangle[0]); double y1 = Double.parseDouble(triangle[1]); double x2 = Double.parseDouble(triangle[2]); double y2 = Double.parseDouble(triangle[3]); double x3 = Double.parseDouble(triangle[4]); double y3 = Double.parseDouble(triangle[5]); double xp = Double.parseDouble(triangle[6]); double yp = Double.parseDouble(triangle[7]); double ax = (x1 - x2); double ay = (y1 - y2); double a = Math.sqrt(ax * ax + ay * ay); double bx = (x2 - x3); double by = (y2 - y3); double b = Math.sqrt(bx * bx + by * by); double cx = (x3 - x1); double cy = (y3 - y1); double c = Math.sqrt(cx * cx + cy * cy); double radius = (a * b * c) / (Math.sqrt((a + b + c) * (-a + b + c) * (a - b + c) * (a + b - c))); double a1 = 2 * (x2 - x1); double b1 = 2 * (y2 - y1); double c1 = (x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2); double a2 = 2 * (x3 - x1); double b2 = 2 * (y3 - y1); double c2 = (x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3); double centerX = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1); double centerY = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1); double distanceX = (centerX - xp); double distanceY = (centerY - yp); double distance = Math.sqrt(distanceX * distanceX + distanceY * distanceY); if (radius > distance) { System.out.println("YES"); } else { System.out.println("NO"); } br.close(); } }