인프런 커뮤니티 질문&답변

숫자를 일일이 포문을 통해 소수를 구하는게 비효율적인 것 같아 다음과 같이 풀어봤는데,, 어떤지 의견이 궁금합니다.

import java.util.Scanner;

public class Main {

    public static void main(String[] args){
        Main main = new Main();
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int[] numbers = new int[number];
        for(int i = 0; i < number; i++){
            numbers[i] = sc.nextInt();
        }
        main.solution(number, numbers);
    }

    public void solution(int number, int[] numbers){
        // get reversed array
        int biggest = 0; // get biggest number for prime
        int[] reversedArr = new int[number];
        
        for (int i = 0; i < number; i++) {
            int tmp = numbers[i];
            int res = 0;
            while (tmp > 0) {
                int t = tmp % 10;
                res = res * 10 + t;
                tmp /= 10;
            }
            reversedArr[i] = res;
            if (res > biggest) biggest = res;
        }
        // prime logic by biggest number
        boolean[] prime = new boolean[biggest + 1]; // add 1 for including 0 --> it means index number is same as each value;
        prime[0] = prime[1] = true; // true = non-prime number
        for (int i = 2; i*i <= biggest; i++){
            if(!prime[i]){
                for (int j = i*i; j <= biggest; j += i){
                    prime[j] = true;
                }
            }
        }
        
        //get result
        for (int i = 0; i < number; i++){
            int target = reversedArr[i];
            if (!prime[target]) System.out.print(target + " ");
        }
    }
}