소수상수근 - 9421번

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내 코드

package com.company;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashSet;
import java.util.Stack;
import java.util.StringTokenizer;

public class Main {
    static HashSet<Integer> set = new HashSet<>();

    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int N = Integer.parseInt(br.readLine());
        boolean[] arr = new boolean[N + 1];

        for (int i = 2; i <= N; i++) {
            int x = i * 2;
            while (x <= N) {
                arr[x] = true;
                x += i;
            }
        }
        for (int i = 3; i <= N; i++) {
            if (!arr[i]) {
                if (check(i)) {
                    System.out.println(i);
                }
            }
        }

    }


    static boolean check(int n) {
        set.clear();
        int temp = n;
        int x = n;
        while (true) {
            temp = x;
            x = 0;
            set.add(temp);
            while (temp > 0) {
                x += (temp % 10) * (temp % 10);
                temp /= 10;
            }

            if (x == 1) {
                return true;
            }
            if (set.contains(x)) {
                return false;
            }

        }
    }
}