백준 1759번 암호 만들기 [ Java ]

1759번: 암호 만들기

import java.io.*;
import java.util.*;

public class Main {
    static int n, r;
    static char[] ch;
    static char[] in;
    static boolean[] visited;
    static StringBuilder sb = new StringBuilder();
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        r = Integer.parseInt(st.nextToken());
        n = Integer.parseInt(st.nextToken());
        in = br.readLine().replace(" ","").toCharArray();
        Arrays.sort(in);
        ch = new char[r];
        visited = new boolean[n];
        bt(0, 0);
        System.out.print(sb);
    }
    static void bt(int depth, int start){
        if (depth == r){
            int vowel = 0;
            int consonant = 0;
            for (char c : ch)
                switch (c){
                    case 'a':
                    case 'e':
                    case 'i':
                    case 'o':
                    case 'u':
                        vowel++;
                        break;
                    default:
                        consonant++;
                }
            if (vowel>=1 && consonant>=2)
                sb.append(String.valueOf(ch)+"\n");
            return;
        }
        for (int i=start; i<n; i++){
            if (!visited[i]){
                visited[i] = true;
                ch[depth] = in[i];
                bt(depth+1, i+1);
                visited[i] = false;
            }
        }
    }
}