PAT 乙级 1054. 求平均值 (20) Java版

本题的基本要求非常简单：给定N个实数，计算它们的平均值。但复杂的是有些输入数据可能是非法的。一个“合法”的输入是[-1000，1000]区间内的实数，并且最多精确到小数点后2位。当你计算平均值的时候，不能把那些非法的数据算在内。

输入格式：

输入第一行给出正整数N（<=100）。随后一行给出N个正整数，数字间以一个空格分隔。

输出格式：

对每个非法输入，在一行中输出“ERROR: X is not a legal number”，其中X是输入。最后在一行中输出结果：“The average of K numbers is Y”，其中K是合法输入的个数，Y是它们的平均值，精确到小数点后2位。如果平均值无法计算，则用“Undefined”替换Y。如果K为1，则输出“The average of 1 number is Y”。

输入样例1：

7
5 -3.2 aaa 9999 2.3.4 7.123 2.35

1 2	7 5 -3.2 aaa 9999 2.3.4 7.123 2.35

输出样例1：

ERROR: aaa is not a legal number
ERROR: 9999 is not a legal number
ERROR: 2.3.4 is not a legal number
ERROR: 7.123 is not a legal number
The average of 3 numbers is 1.38

ERROR: aaa is not a legal number

ERROR: 9999 is not a legal number

ERROR: 2.3.4 is not a legal number

ERROR: 7.123 is not a legal number

The average of 3 numbers is 1.38

输入样例2：

2
aaa -9999

1 2	2 aaa -9999

输出样例2：

ERROR: aaa is not a legal number
ERROR: -9999 is not a legal number
The average of 0 numbers is Undefined

ERROR: aaa is not a legal number

ERROR: -9999 is not a legal number

The average of 0 numbers is Undefined

这里用了抛异常的方式来判断输入的值是否符合规则

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int cnt = 0;
		double y = 0;
		for (int i = 0; i < n; i++) {
			double x = 0;
			String s = null;
			try {
				s = in.next();
				x = Double.parseDouble(s);
				double temp = Double.parseDouble(String.format("%.2f", x));
				if (x > 1000 || x < -1000 || Math.abs(temp - x) >= 0.001) {
					throw new NumberFormatException();
				}

				cnt++;
				y += x;
			} catch (NumberFormatException e) {
				System.out.println("ERROR: " + s + " is not a legal number");
			}
		}
		in.close();

		if (cnt == 0) {
			System.out.println("The average of 0 numbers is Undefined");
		} else if (cnt == 1) {
			System.out.printf("The average of 1 number is %.2f", y);
		} else {
			System.out.printf("The average of %d numbers is %.2f", cnt, y / cnt);
		}
	}

}

import java.util.Scanner;

public class Main {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int n = in.nextInt();

int cnt = 0;

double y = 0;

for (int i = 0; i < n; i++) {

double x = 0;

String s = null;

try {

s = in.next();

x = Double.parseDouble(s);

double temp = Double.parseDouble(String.format("%.2f", x));

if (x > 1000 || x < -1000 || Math.abs(temp - x) >= 0.001) {

throw new NumberFormatException();

}

cnt++;

y += x;

} catch (NumberFormatException e) {

System.out.println("ERROR: " + s + " is not a legal number");

}

in.close();

if (cnt == 0) {

System.out.println("The average of 0 numbers is Undefined");

} else if (cnt == 1) {

System.out.printf("The average of 1 number is %.2f", y);

} else {

System.out.printf("The average of %d numbers is %.2f", cnt, y / cnt);

}

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