PAT 1152 Google Recruitment

1152 Google Recruitment (20 分)

In July 2004, Google posted on a giant billboard along Highway 101 in Silicon Valley (shown in the picture below) for recruitment. The content is super-simple, a URL consisting of the first 10-digit prime found in consecutive digits of the natural constant

The natural constant

Now you are asked to solve a more general problem: find the first K-digit prime in consecutive digits of any given L-digit number.

Input Specification:

Each input file contains one test case. Each case first gives in a line two positive integers: L ( $\leq 1,000) and K (< 10), which are the numbers of digits of the given number and the prime to be found, respectively. Then the L-digit number N is given in the next line.$

Output Specification:

For each test case, print in a line the first K-digit prime in consecutive digits of N. If such a number does not exist, output 404 instead. Note: the leading zeroes must also be counted as part of the K digits. For example, to find the 4-digit prime in 200236, 0023 is a solution. However the first digit 2 must not be treated as a solution 0002 since the leading zeroes are not in the original number.

Sample Input 1:

20 5
23654987725541023819

Sample Output 1:

Sample Input 2:

10 3
2468024680

Sample Output 2:

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;


ll to_int(string s){
    ll sum = 0;
    for(int i=0;i < s.size();i++){
        sum = sum*10+(s[i]-'0');
    }
    return sum;
}


bool is_prime(ll x){
    for(int i=2;i <= sqrt(x);i++){
        if(x%i == 0) return false;
    }
    return true;
}



int main(){
    int len,n;
    cin >> len >> n;
    string s;
    cin >> s;

    int flag = 1;
    for(int i=0;i <= len-n;i++){
        string temp = s.substr(i,n);
        ll num = to_int(temp);
        if(is_prime(num)){
            cout << temp;
            flag = 0;
            break;
        }
    }

    if(flag) cout << 404;



    return 0;
}

_一开始想复杂了以为要筛一下，其实直接判断素数就可以了，因为长度限制在1000以内，1000*10^5 = 10^8不会爆掉

噢对了，用stastic int可以申请到更大的空间数组（静态空间大小），用malloc申请到的更大（磁盘区大小），普通的数组是在栈空间申请，比较小。