There are several ways to determine whether a number is a prime number:
(1)Use between 2 and number-1 All numbers are divided by number. If one is divisible, it means that number is a non-prime number; unless all numbers are not divisible, it means that number is a prime number. # Prime number; unless all numbers are not divisible, the number is prime. (3) Use all numbers between 2 and the square root of number to divide number. If any number can be divided evenly, it means that number is a non-prime number; unless all numbers cannot be divided evenly, it means that number is a prime number. .
The efficiency of these three methods is gradually improved. The implementation of the third method is listed below:import java.util.Scanner; public class Test2 { public static void main(String[] args) { int number; // 输入的数字 Scanner input = new Scanner(System.in); System.out.println("请输入数字"); number = input.nextInt(); // 输入数字 if(isPrimeNumber(number)){ System.out.println(number + "是一个素数"); } else{ System.out.println(number + "是一个非素数"); } } public static boolean isPrimeNumber(int num){ if(num < 2){ System.out.println("数据错误"); return false; } int k = (int)Math.sqrt(num); //num的平方根 int i; for(i=2; i<=k; i++){ //依次用2..k之间的数去整除num,如果没有一个数能被整除,说明num是素数 if(num % i == 0){ break; } } if(i > k){ return true; } return false; } }
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