[PAT-A] 1152 Google Recruitment

Java

import java.io.*;
import java.util.*;

public class Main {
    static boolean isPrime(int n) {
        if (n <= 1) {
            return false;
        }
        for (int i = 2; i <= n / i; i++) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int len = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();

        for (int i = 0; i <= len - k; i++) {
            String substr = s.substring(i, i + k);
            int num = Integer.parseInt(substr);

            if (isPrime(num)) {
                System.out.println(substr);
                return;
            }
        }

        System.out.println("404");
    }
}

C++

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int len, k;
string s;

bool is_prime(int n) {
    if (n <= 1) return false;
    for (int i = 2; i <= n / i; ++i)
        if (n % i == 0) return false;
    return true;
}

int main() {
    cin >> len >> k >> s;

    for (int i = 0; i < len - k + 1; ++i) {
        string subs = s.substr(i, k);
        int x = stoi(subs);
        if (is_prime(x)) {
            cout << subs << endl;
            return 0;
        }
    }

    cout << "404" << endl;
    return 0;
}