腾讯2017校招编程：一个数等于两个素数的和

import java.util.ArrayList;
import java.util.Scanner;


public class qq001 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n;
		ArrayList<Integer> prime=primes(1000);
//		System.out.println(prime);
		while(in.hasNext()){
			n = in.nextInt();
			System.out.println(countPrimeSum(prime,n));
		}
	}
	private static int countPrimeSum(ArrayList<Integer> prime,int n){
		int i=0;
		int j=prime.size() - 1;
		int count = 0;
		while(i<=j){
			int t = prime.get(i) + prime.get(j);
			if(t==n){
//				System.out.println(prime.get(i)+" "+prime.get(j));
				count++;
				i++;
				j--;
			}else if(t<n){
				i++;
			}else{
				j--;
			}
		}
		return count;
	}
	private static ArrayList<Integer> primes(int n){
		ArrayList<Integer> prime = new ArrayList<Integer>();
		prime.add(2);
		prime.add(3);
		for(int i=4;i<=n;i++){
			boolean flag = true;
			for(int j=0;j<prime.size();j++){
				if(i%prime.get(j) == 0){
					flag = false;
					break;
				}
			}
			if(flag){
				prime.add(i);
			}
		}
		return prime;
	}

}