全排列模板

1.回溯法-dfs（sort后，然后dfs，数列是按字典序的）

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

public class Main {
       static int n;
       static final int max=1005;
       static boolean vis[]=new boolean [max];
       static int a[]=new int[max];
       static int b[]=new int[max];
       public static void dfs(int step){
             if(step==n){
                 for(int i=0;i<n;i++) System.out.print(b[i]);
                 System.out.println();
             }
             for(int i=0;i<n;i++){
                   if(!vis[i]){
                         vis[i]=true;
                         b[step]=a[i];
                         dfs(step+1);
                         vis[i]=false;
                   }
             }
       }
       public static void main(String[] args) {
            Scanner scan=new Scanner(System.in);
            n=scan.nextInt();
            for(int i=0;i<n;i++) a[i]=scan.nextInt();
            Arrays.sort(a,0,n);
            dfs(0); 
    }
}

2.递归法（不按字典序）

import java.util.Arrays;

public class Main {
     public static void print(int arr[],int n){
          for(int i=0;i<=n;i++)
              System.out.print(arr[i]);
          System.out.println();
     }
     public static void swap(int arr[],int i,int p){
         int t=arr[i];
         arr[i]=arr[p];
         arr[p]=t;
     }
      public static void allSort(int arr[],int p,int q){
            if(p==q){
                 print(arr,q);
            }
            else{
                for(int i=p;i<=q;i++){
                    swap(arr,i,p);
                    allSort(arr,p+1,q);
                    swap(arr,i,p);
                }
            }
      }
     public static void main(String[] args) {
          int arr[]={1,2,3,4};
          Arrays.sort(arr,0,arr.length);
          allSort(arr,0,arr.length-1);
    }
}