[백준] 1759번 암호 만들기

import java.util.Arrays;
import java.util.Scanner;

public class Main {
    static int L, M;
    static char[] arr;
    static char[] selected;
    static StringBuilder sb = new StringBuilder();

    static boolean isValid() {
        int consonant = 0, vowel = 0;

        for (int i = 1; i <= L; i++) {
            char x = selected[i];
            if (x == 'a' || x == 'e' || x == 'i' || x == 'o' || x == 'u') {
                vowel++;
            } else {
                consonant++;
            }
        }

        return consonant >= 2 && vowel >= 1;
    }

    static void rec_func(int k, int index) {
        if (k == L + 1) {
            if (isValid()) {
                for (int i = 1; i <= L; i++) {
                    sb.append(selected[i]);
                }
                sb.append('\n');
            }
            return;
        }

        for (int i = index; i <= M; i++) {
            selected[k] = arr[i];
            rec_func(k + 1, i + 1);
            selected[k] = '\0';
        }
    }

    public static void main(String[] args) {
        Scanner kb = new Scanner(System.in);

        L = kb.nextInt();
        M = kb.nextInt();

        arr = new char[M + 1];
        selected = new char[L + 1];

        for (int i = 1; i <= M; i++) {
            arr[i] = kb.next().charAt(0);
        }

        Arrays.sort(arr, 1, M + 1);

        rec_func(1, 1);
        System.out.println(sb.toString());
    }
}