Java实现 洛谷 P1036 选数

import java.util.Scanner;
 
public class Main {
	private static Scanner cin;
	private static int[] numbers ;
	private static int counter = 0;
	
	public static void main(String args[]) throws Exception {
		cin = new Scanner(System.in);
		int n = cin.nextInt();
		int k = cin.nextInt();
		numbers = new int[n];
		for(int i=0;i<n;i++) {
			numbers[i] = cin.nextInt();
		}
		for(int i=0;i<n-k+1;i++) {
			Main.calc(n,i,k,0,String.valueOf(i));
		}
		System.out.println(counter);
	}
	
	public  static void calc(int n,int start, int k,int ret,String value) {
		int sum = 0;
		if(n-start <k ) {
			return;
		}
		if (k == 1) {
			sum = ret + numbers[start];
			if(testIsPrime(sum)) {
				counter++;
			}
		}else {
			sum = ret+numbers[start];
			for (int i=start;i<n;i++) {
				calc(n,i+1,k-1,sum,value+"-"+i);
			}
		}
	}
	
	 public static boolean testIsPrime(int n){
	       if (n <= 3) {
	            return n > 1;
	        }
	        
	       for(int i=2;i<=Math.sqrt(n);i++){
	           if(n%i == 0)
	               return false;
	       }
	       return true;
	   }
}