1108 Finding Average （PAT甲级）

#include 
#include 
#include 
#include 

bool judge(std::string str){
    int cnt = 0;
    std::string s = ".";
    for(int i = 0; i < str.size(); ++i){
        if((str[i] < '0' || str[i] > '9') && str[i] != '.' && str[i] != '-'){
            return false;
        }
        if(str[i] == '.'){
            ++cnt;
        }
    }
    if(cnt > 1){
        return false;
    }
    int pos = str.find(s);
    if(pos != -1 && str.size() - pos > 3){
        return false;
    }
    if(std::stod(str) < -1000 || std::stod(str) > 1000){
        return false;
    }
    return true;
}

int main(){
    int N, cnt;
    double sum;
    std::string str;
    scanf("%d", &N);
    sum = 0;
    cnt = 0;
    for(int i = 0; i < N; ++i){
        std::cin >> str;
        if(!judge(str)){
            printf("ERROR: %s is not a legal number\n", str.c_str());
        } else{
            ++cnt;
            sum += std::stod(str);
        }
    }
    if(cnt == 0){
        printf("The average of %d numbers is Undefined", cnt);
    } else if(cnt == 1){
        printf("The average of 1 number is %.2f", sum);
    } else{
        printf("The average of %d numbers is %.2f", cnt, sum / cnt);
    }
    return 0;
}

参考柳婼解法：

#include 
#include 
#include 
#include 

bool judge(std::string str){
    double a;
    char ss[50];
    sscanf(str.c_str(), "%lf", &a);
    sprintf(ss, "%.2f", a);
    for(int i = 0; i < str.size(); ++i){
        if(ss[i] != str[i]){
            return false;
        }
    }
    if(std::stod(str) < -1000 || std::stod(str) > 1000){
        return false;
    }
    return true;
}

int main(){
    int N, cnt;
    double sum;
    std::string str;
    scanf("%d", &N);
    sum = 0;
    cnt = 0;
    for(int i = 0; i < N; ++i){
        std::cin >> str;
        if(!judge(str)){
            printf("ERROR: %s is not a legal number\n", str.c_str());
        } else{
            ++cnt;
            sum += std::stod(str);
        }
    }
    if(cnt == 0){
        printf("The average of %d numbers is Undefined", cnt);
    } else if(cnt == 1){
        printf("The average of 1 number is %.2f", sum);
    } else{
        printf("The average of %d numbers is %.2f", cnt, sum / cnt);
    }
    return 0;
}

题目如下：

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 [−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:

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