要排个序真的坑，我的垃圾ac代码。。。 ```java public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = in.nextInt(); // 圆的数量 boolean jishu = false; int[] r = new int[n]; for (int i = 0; i < n; i++) { r[i] = in.nextInt(); } Arrays.sort(r); if ((n & 1) == 1) jishu = true; // 最里面是黑色的 double[] s = new double[n]; for (int i = 0; i < n;i++) { int radius = r[i]; s[i] = Math.PI * radius * radius; } BigDecimal res = new BigDecimal(0); for (int i = n-1; i >=1 ;i-=2) { res = res.add(new BigDecimal(s[i] - s[i-1])); } if (jishu) { res = res.add(new BigDecimal(s[0])); } DecimalFormat format = new DecimalFormat("#0.00000"); System.out.println(format.format(res)); } ```