讀檔&找質數

Q3找質數.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

// 找質數
public class Q940303 {
	public static void main(String[] args) throws FileNotFoundException {
		String fileName = "940303.SM";
		File f = new File(fileName);
		Scanner sc = new Scanner(f);
		while (sc.hasNext()){
			int n = sc.nextInt();
			System.out.print(n + " ");
			if (isPrime(n))
				System.out.println("is a prime number.");
			else
				System.out.println("is not a prime number.");
		}
		sc.close();
	}
	
	public static boolean isPrime(int n){
		for (int i=2; i<n; i++){
			if (i*i>=n) break; // 若 i^2 > n 則停
			if (n%i == 0) return false;
		}
		return true;
	}

}