PAT 甲级 1108 Finding Average (20分)

1108 Finding Average (20分)

 

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 legal input is a real number in [−] 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 (≤). 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:

7
5 -3.2 aaa 9999 2.3.4 7.123 2.35

 

Sample Output 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

 

Sample Input 2:

2
aaa -9999

 

Sample Output 2:

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

 

作者: CHEN, Yue

单位: 浙江大学

时间限制: 400 ms

内存限制: 64 MB

代码长度限制: 16 KB

题意：

给出一组数据，判断输出是不是合法数字（精度不超过小数点后两位，范围【-1000，1000】），有合法数据还要累加算出average；不存在合法数据输出The average of 0 numbers is Undefined

题解：

第一发没过原因是number和numbers没有看清楚。k=0,1,>1要分开讨论。

注意细节：详见代码注释。

AC代码：

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    int k=0;
    double sum=0;
    string a;
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a;
        double add=0;
        int l=a.length();
        int fu=0;
        int p=-1;
        int legal=1;
        for(int i=0;i<l;i++){
            if(i==0){
                if(a[i]=='-'){
                    fu=1;
                    continue;
                }
            }
            if(a[i]=='.'){
                if(p!=-1){//记录小数点位置 
                    legal=0;
                    break;
                }else{
                    p=i;
                    if(l-i>3){//小数点后有三位了，不合法 
                        legal=0;
                        break;
                    }
                }
            }else if(a[i]>='0'&&a[i]<='9'){
                if(p!=-1&&i-p==1){//小数点后两位特殊处理 
                    add=add+(a[i]-'0')*0.1;
                }else if(p!=-1&&i-p==2){
                    add=add+(a[i]-'0')*0.01;
                }else{
                    add=add*10+a[i]-'0';
                }
                if(abs(add)>1000){//数过大或过小 
                    legal=0;
                    break;
                }            
            }else{
                legal=0;
                break;
            }
        }        
        if(!legal){
            printf("ERROR: %s is not a legal number
",a.c_str());
        }else{
            if(fu==1) add=0-add;//负数    
            sum+=add;
            k++;
        }
    }
    if(k==0){
        printf("The average of 0 numbers is Undefined");
    }else if(k==1){
        printf("The average of %d number is %.2lf",k,sum/k);
    }else{
        printf("The average of %d numbers is %.2lf",k,sum/k);
    }    
    return 0;
}