import java.util.Arrays; //利用二进制算法进行全排列 //count1:170187 //count2:291656 public class test {     public static void main(String[] args) {         long start=System.currentTimeMillis();         count2();         long end=System.currentTimeMillis();         System.out.println(end-start);     }     private static void count2(){         int[] num=new int []{1,2,3,4,5,6,7,8,9};         for(int i=1;i<Math.pow(9, 9);i++){             String str=Integer.toString(i,9);             int sz=str.length();             for(int j=0;j<9-sz;j++){                 str="0"+str;             }             char[] temp=str.toCharArray();             Arrays.sort(temp);             String gl=new String(temp);             if(!gl.equals("012345678")){                 continue;             }             String result="";             for(int m=0;m<str.length();m++){                 result+=num[Integer.parseInt(str.charAt(m)+"")];             }             System.out.println(result);         }     }     public static void count1(){         int[] num=new int []{1,2,3,4,5,6,7,8,9};         int[] ss=new int []{0,1,2,3,4,5,6,7,8};         int[] temp=new int[9];         while(temp[0]<9){             temp[temp.length-1]++;             for(int i=temp.length-1;i>0;i--){                 if(temp[i]==9){                     temp[i]=0;                     temp[i-1]++;                 }             }             int []tt=temp.clone();             Arrays.sort(tt);             if(!Arrays.equals(tt,ss)){                 continue;             }             String result="";             for(int i=0;i<num.length;i++){                 result+=num[temp[i]];             }             System.out.println(result);         }     } }

package practice; import java.util.ArrayList; import java.util.List; public class Test1 {     /**      * @param args      */     public static void main(String[] args) {         // TODO Auto-generated method stub         Object[] tmp={1,2,3,4,5,6}; //        ArrayList<Object[]> rs=RandomC(tmp);         ArrayList<Object[]> rs=cmn(tmp,3);         for(int i=0;i<rs.size();i++)         { //            System.out.print(i+"=");             for(int j=0;j<rs.get(i).length;j++)             {                 System.out.print(rs.get(i)[j]+",");             }             System.out.println();         }     }         // 求一个数组的任意组合     static ArrayList<Object[]> RandomC(Object[] source)     {         ArrayList<Object[]> result=new ArrayList<Object[]>();         if(source.length==1)         {             result.add(source);                }         else         {             Object[] psource=new Object[source.length-1];             for(int i=0;i<psource.length;i++)             {                 psource[i]=source[i];             }             result=RandomC(psource);             int len=result.size();//fn组合的长度             result.add((new Object[]{source[source.length-1]}));             for(int i=0;i<len;i++)             {                 Object[] tmp=new Object[result.get(i).length+1];                 for(int j=0;j<tmp.length-1;j++)                 {                     tmp[j]=result.get(i)[j];                 }                 tmp[tmp.length-1]=source[source.length-1];                 result.add(tmp);             }         }         return result;     }     static ArrayList<Object[]> cmn(Object[] source,int n)     {         ArrayList<Object[]> result=new ArrayList<Object[]>();         if(n==1)         {             for(int i=0;i<source.length;i++)             {                 result.add(new Object[]{source[i]});             }         }         else if(source.length==n)         {             result.add(source);         }         else         {             Object[] psource=new Object[source.length-1];             for(int i=0;i<psource.length;i++)             {                 psource[i]=source[i];             }             result=cmn(psource,n);             ArrayList<Object[]> tmp=cmn(psource,n-1);             for(int i=0;i<tmp.size();i++)             {                 Object[] rs=new Object[n];                 for(int j=0;j<n-1;j++)                 {                     rs[j]=tmp.get(i)[j];                 }                 rs[n-1]=source[source.length-1];                 result.add(rs);             }         }         return result;     } }

package Acm; //强大的求组合数 public class MainApp {     public static void main(String[] args) {         int[] num=new int[]{1,2,3,4,5};         String str="";         //求3个数的组合个数 //        count(0,str,num,3); //        求1-n个数的组合个数         count1(0,str,num);     }     private static void count1(int i, String str, int[] num) {         if(i==num.length){             System.out.println(str);             return;         }         count1(i+1,str,num);         count1(i+1,str+num[i]+",",num);     }     private static void count(int i, String str, int[] num,int n) {         if(n==0){             System.out.println(str);             return;         }         if(i==num.length){             return;         }         count(i+1,str+num[i]+",",num,n-1);         count(i+1,str,num,n);     } }

package Acm; //求排列，求各种排列或组合后排列 import java.util.Arrays; import java.util.Scanner; public class Demo19 {     private static boolean f[];     public static void main(String[] args) {         Scanner sc=new Scanner(System.in);         int sz=sc.nextInt();         for(int i=0;i<sz;i++){             int sum=sc.nextInt();             f=new boolean[sum];             Arrays.fill(f, true);             int[] num=new int[sum];             for(int j=0;j<sum;j++){                 num[j]=j+1;             }             int nn=sc.nextInt();             String str="";             count(num,str,nn);         }     }     /**      *      * @param num 表示要排列的数组      * @param str 以排列好的字符串      * @param nn  剩下需要排列的个数，如果需要全排列，则nn为数组长度      */     private static void count(int[] num, String str, int nn) {         if(nn==0){             System.out.println(str);             return;         }         for(int i=0;i<num.length;i++){             if(!f[i]){                 continue;             }             f[i]=false;             count(num,str+num[i],nn-1);             f[i]=true;         }     } }