[프로그래머스] 소수 찾기 - JAVA

문제

https://school.programmers.co.kr/learn/courses/30/lessons/42839

프로그래머스

 

코드

import java.util.*;

class Solution {
    static boolean visited[];
    static Set<Integer> set = new HashSet<>();
    
    public int solution(String numbers) {
        int answer = 0;
        visited = new boolean[numbers.length()];
        back(numbers, "");
        
        Iterator<Integer> it = set.iterator();
        while(it.hasNext()){
            if(find(it.next())) answer += 1;
        }
        return answer;
    }
    
    public void back(String numbers, String str){
        if(!str.equals("") && str.length() <= numbers.length()){
            int num = Integer.parseInt(str);
            set.add(num);
            System.out.println(str);
        }
        for(int i=0;i<numbers.length();i++){
            if(!visited[i]){
                visited[i] = true;
                 back(numbers, str + numbers.charAt(i));
                visited[i] = false;
            }
           
        }
    }
   
    public boolean find(int num){
        if(num == 0 || num == 1) return false;
        for(int i=2;i*i<=num;i++){
            if(num % i == 0) return false;
        }
        return true;
    }

}