题目

The basic task is simple: given N real numbers, you are supposed to calculate their average. But what makes it complicated is that some of the input numbers might not be legal. A legalinput is a real number in [−1000,1000] and is accurate up to no more than 2 decimal places. When you calculate the average, those illegal numbers must not be counted in.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤100). Then N numbers are given in the next line, separated by one space.

Output Specification:

For each illegal input number, print in a line ERROR: X is not a legal number where X is the input. Then finally print in a line the result: The average of K numbers is Y where K is the number of legal inputs and Y is their average, accurate to 2 decimal places. In case the average cannot be calculated, output Undefined instead of Y. In case K is only 1, output The average of 1 number is Y instead.

Sample Input 1:

1
2

7
5 -3.2 aaa 9999 2.3.4 7.123 2.35

Sample Output 1:

1
2
3
4
5

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

Sample Input 2:

1
2

2
aaa -9999

Sample Output 2:

1
2
3

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

题解

思路

• 难度没什么
• 就是复杂，就是绕
• 不过好在样例里已经把所有的异常情况告诉你了
• 照着情况排除就可以了

数据结构

• nums 存放所有的数（以字符串的形式）
• ans 存放所有合法的数

算法

• 写了一个check() 函数辅助判断一个字符串是否合法。
• 可以不写，我只是为了结构清晰一点。因为一次return后面的就不执行了。
• 根据ans的长度来判断合适的输出
• 异常情况处理就是
  • 当字符串不含有小数点 或者 （字符串含有一个小数点且小数点后字符小于等于2位）
  • 且大小在正负1000以内
  • 返回True
• 其他情况返回False

代码

• 因为使用Python可以AC，因此只放了Python的解。

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def check(string):
    if all([i in "-1234567890." for i in string]):
        if ((string.count(".") == 0) or (
                string.count(".") == 1 and len(string) - string.index(".") <= 3)) and -1000 <= float(string) <= 1000:
            return True
    return False


n = int(input())
nums = input().split()
ans = []
for i in nums:
    if check(i):
        ans.append(float(i))
    else:
        print("ERROR: %s is not a legal number" % i)
if len(ans) == 0:
    print("The average of 0 numbers is Undefined")
elif len(ans) == 1:
    print("The average of 1 number is %.2f" % float(ans[0]))
else:
    print("The average of %d numbers is %.2f" % (len(ans), sum(ans) / len(ans)))