HDACM 1785
直接调用Math.atan2（）方法即可
import java.util.Scanner;public class Main{public static void main(String[] args) {Scanner sc = new Scanner(System.in);while(sc.hasNext()){int n = sc.nextInt();if (n<0) {break;}double point[][] = new double[n][3];for (int i = 0; i < n; i++) {point[i][0]=sc.nextDouble();point[i][1]=sc.nextDouble();point[i][2] = Math.atan2(point[i][1],point[i][0]);}for (int i = 0; i < point.length-1; i++) {for (int j = i+1; j < point.length; j++) {if (point[i][2]>point[j][2]) {double temp = point[i][0];point[i][0] = point[j][0];point[j][0] = temp;temp = point[i][1];point[i][1] = point[j][1];point[j][1] = temp;temp = point[i][2];point[i][2] = point[j][2];point[j][2] = temp;}}}System.out.printf("%.1f %.1f",point[0][0],point[0][1]);for (int i = 1; i < point.length; i++) {System.out.printf(" %.1f %.1f",point[i][0],point[i][1]);}System.out.println();}sc.close();}
}