순열, DFS

✅ 1부터 10 사이의 자연수 m개가 주어졌을 때, n개를 뽑을 수 있는 경우의 수를 모두 구하세요.

//⭐️input:
//자연수 개수 m, 뽑을 숫자 개수 n
//들어온 자연수
3 2
3 6 9

//⭐️output:
3 6
3 9
6 3
6 9
9 3
9 6

🔵 How to solve

🟢 Code

class Main {
        static int n;
        static int m;
        static int[] intArr;
        static int[] ch;
        static int[] answer;

        public void DFS(int L) {
            if(L==m){
                for(int x: answer){
                    System.out.print(x + " ");
                }
                System.out.println();
            }else{
                for(int i=0; i<n; i++){
                    if(ch[i] == 0) {
                        ch[i] = 1;
                        answer[L] = intArr[i]; //⭐️
                        DFS(L+1);
                        ch[i]=0; //체크 풀어주기
                    }
                }
            }
        }

        public static void main(String[] args) {
            Main T = new Main();
            Scanner sc = new Scanner(System.in);
            n= sc.nextInt();
            m= sc.nextInt();
            intArr= new int[n];
            ch= new int[n];
            answer= new int[m];
            for(int i=0; i<n; i++){
                intArr[i] = sc.nextInt();
            }
            T.DFS(0);

        }
}

⭐️ What I learned

In this part, answer[L] = intArr[i]
I first made the code like answer[i] = intArr[i], and thus got a 🔴zero-exit error.
it was because array answer only has up to n size whereas i is up to m,
and since mis bigger than n, (m=3, n=2 in this case)
I got the 🔴zero-exit error.

Then, my question was how to get to answer index?!
The solution to this problem was using L, which is the Level that the DFS is in right now,
which also matches the index of the array.