public class demo1 { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); while (scanner.hasNext()) { int num = scanner.nextInt(); if (num == 0) { System.out.println("end"); return; } //num可以拆为多少组质数相加 //eg：18 7+11 5+13 //优化，直接通过减法 int count = 0; for (int i = 2; i<= num /2 ;i++) { int target = num - i; if (isPrime(target) && isPrime(i)) { count++; } } System.out.println(count); } } private static boolean isPrime(int num) { for (int i = 2; i <= Math.sqrt(num) ; i++) { if (num%i == 0) { return false; } } return true; } }