public class Main {
    static int N = 4;
    static int[] solution = new int[N];
    static int[] use = new int[N];

    public static void main(String[] args){
        backtrack(0);
    }


    public static void backtrack(int n){
        System.out.println(n);

        if(n==N){
            System.out.println("=====================================");
            StringBuffer sb = new StringBuffer();
            for(int i=0; i<N; i++){
                sb.append(solution[i]).append(", ");
            }
            System.out.println(sb.toString());
            System.out.println("=====================================");
            return;
        }

        for(int i=0; i<N; i++){
            System.out.println("n : "+n+", i : "+i);

            if(use[i] == 0){
                solution[n] = i+1;
                use[i] = 1;
                backtrack(n+1);
                use[i] = 0;
            }
        }
    }
}