[Java] 프로그래머스 - 소수 찾기

1월 29일(월) - 6장 완전 탐색

프로그래머스

---

import java.util.*;
import java.util.stream.Collectors;


public class Solution {

    private boolean is_prime(int n){
        if(n <= 1)
        {
            return false;
        }
        for(int i=2; i*i<=n; i++)
        {
            if(n%i == 0)
            {
                return false;
            }
        }
        return true;
    }

    private Set<Integer> get_prime(int acc, List<Integer> numbers){
        Set<Integer> primes = new HashSet<>();
        if(is_prime(acc))
        {
            primes.add(acc);
        }

        for(int i=0; i<numbers.size(); i++)
        {
            int next_acc = acc * 10 + numbers.get(i);
            List<Integer> next_number = new ArrayList<>(numbers);
            next_number.remove(i);
            primes.addAll(get_prime(next_acc, next_number));
        }

        return primes;
    }

    public int solution(String nums){
        List<Integer> numbers = nums.chars()
                .map(c -> c - '0')
                .boxed()
                .collect(Collectors.toList());
        return get_prime(0,numbers).size();
    }
}

---