[プログラマー]少数を検索

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Code

import java.util.*;

class Solution {
    public int solution(String numbers) {
        int answer = 0;
        HashSet<Integer> set = new HashSet<>();
        permutation("", numbers, set);
        Iterator<Integer> iter = set.iterator();
        while (iter.hasNext()) {
            int next = iter.next();
            if (next == 2 || (next % 2 != 0 && isPrime(next))) {
                answer++;
            }
        }
        return answer;
    }

    public void permutation(String prefix,String str, HashSet<Integer> set) {
        if (!prefix.equals("")) {
            set.add(Integer.parseInt(prefix));
        }
        if (str.equals("")) {
            return;
        }
        for (int i = 0; i < str.length(); i++) {
            permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i + 1), set);
        }
    }

    public boolean isPrime(int x) {
        if (x == 0 || x == 1) {
            return false;
        }
        for (int i = 3; i <= (int)Math.sqrt(x); i += 2) {
            if (x % i == 0) {
                return false;
            }
        }
        return true;
    }
}

Solution