JAVA ac代码:

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

public class Main {
    static int n;
    static boolean flag[];//这个数是否被用过
    public static void main(String[] args) {
        n=in.nextInt();
        flag=new boolean[n+1];
        int[] arr=new int[n];//当前数组
        dfs(arr,0);
        out.close();
    }

    
    private static void dfs(int[] arr, int i) {
        //终止条件:i==n,即arr数组中1到n-1位置都被填完了
        if(i==n) {
            for(int j=0;j<n;j++) out.print(arr[j]+" ");
            out.println();
            return;
        }
        
        for(int j=1;j<=n;j++) {
            //j还没被用过
            if(!flag[j]) {
                flag[j]=true;
                arr[i]=j;//赋值
                dfs(arr,i+1);
                //回溯
                arr[i]=0;
                flag[j]=false;
            }
        }
    }


    static FastReader in=new FastReader();
    static PrintWriter out=new PrintWriter(System.out);
    static class FastReader{
        static BufferedReader br;
        static StringTokenizer st;
        FastReader(){
            br=new BufferedReader(new InputStreamReader(System.in));
        }
        String next() {
            String str="";
            while(st==null||!st.hasMoreElements()) {
                try {
                    str=br.readLine();
                }catch(IOException e) {
                    throw new RuntimeException(e);
                }
                st=new StringTokenizer(str);
            }
            return st.nextToken();
        }
        int nextInt() {
            return Integer.parseInt(next());
        }
        double nextDouble() {
            return Double.parseDouble(next());
        }
        long nextLong() {
            return Long.parseLong(next());
        }
    }
    
}