题解 | #素数对#

#include <iostream>
using namespace std;

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

int main() {
    int n;
    cin >> n;
    
    int count = 0;
    for (int i = 2; i <= n/2; i++) {
        if (isPrime(i) && isPrime(n-i)) {
            count++;
        }
    }
    
    cout << count << endl;
    return 0;
}

import java.util.Scanner;

public class Main {
    public static boolean isPrime(int n) {
        if (n < 2) return false;
        for (int i = 2; i * i <= n; i++) {
            if (n % i == 0) return false;
        }
        return true;
    }
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        
        int count = 0;
        for (int i = 2; i <= n/2; i++) {
            if (isPrime(i) && isPrime(n-i)) {
                count++;
            }
        }
        
        System.out.println(count);
    }
}

def is_prime(n):
    if n < 2:
        return False
    i = 2
    while i * i <= n:
        if n % i == 0:
            return False
        i += 1
    return True

n = int(input())
count = 0

for i in range(2, n//2 + 1):
    if is_prime(i) and is_prime(n-i):
        count += 1

print(count)