Sub group

            9 Athletes need to be divided into three groups for preliminary competition.
            //What are the grouping schemes?

            //We mark athletes as A,B,C,... I
            //The following program lists all the grouping methods.

            //The normal output of this program is:
            ABC DEF GHI
            ABC DEG FHI
            ABC DEH FGI
            ABC DEI FGH
            ABC DFG EHI
            ABC DFH EGI
            ABC DFI EGH
            ABC DGH EFI
            ABC DGI EFH
            ABC DHI EFG
            ABC EFG DHI
            ABC EFH DGI
            ABC EFI DGH
            ABC EGH DFI
            ABC EGI DFH
            ABC EHI DFG
            ABC FGH DEI
            ABC FGI DEH
            ABC FHI DEG
            ABC GHI DEF
            ABD CEF GHI
            ABD CEG FHI
            ABD CEH FGI
            ABD CEI FGH
            ABD CFG EHI
            ABD CFH EGI
            ABD CFI EGH
            ABD CGH EFI
            ABD CGI EFH
            ABD CHI EFG
            ABD EFG CHI
            ..... (The following is omitted, 560 lines in total). 

 public class A  
    {  
        public static String remain(int[] a)  
        {  
            String s = "";  
            for(int i=0; i<a.length; i++){  
                if(a[i] == 0) s += (char)(i+'A');  
            }     
            return s;  
        }  

        public static void f(String s, int[] a)  
        {  
            for(int i=0; i<a.length; i++){  
                if(a[i]==1) continue;  
                a[i] = 1;  
                for(int j=i+1; j<a.length; j++){  
                    if(a[j]==1) continue;  
                    a[j]=1;  
                    for(int k=j+1; k<a.length; k++){  
                        if(a[k]==1) continue;  
                        a[k]=1;  
                        System.out.println(__________________________________);  //Fill in position  
                        a[k]=0;  
                    }  
                    a[j]=0;  
                }  
                a[i] = 0;  
            }  
        }  

        public static void main(String[] args)  
        {  
            int[] a = new int[9];         
            a[0] = 1;  

            for(int b=1; b<a.length; b++){  
                a[b] = 1;  
                for(int c=b+1; c<a.length; c++){  
                    a[c] = 1;  
                    String s = "A" + (char)(b+'A') + (char)(c+'A');  
                    f(s,a);  
                    a[c] = 0;  
                }  
                a[b] = 0;  
            }  
        }  
    }  

public class Main  
{  
    public static String remain(int[] a)  
    {  
        String s = "";  
        for(int i=0; i<a.length; i++){  
            if(a[i] == 0) s += (char)(i+'A');  
        }     
        return s;  
    }  

    public static void f(String s, int[] a)  
    {  
        for(int i=0; i<a.length; i++){  
            if(a[i]==1) continue;  
            a[i] = 1;  
            for(int j=i+1; j<a.length; j++){  
                if(a[j]==1) continue;  
                a[j]=1;  
                for(int k=j+1; k<a.length; k++){  
                    if(a[k]==1) continue;  
                    a[k]=1;  
                    System.out.println(s+" "+(char)('A'+i)+(char)('A'+j)+(char)('A'+k)+" "+remain(a));
                    a[k]=0;  
                }  
                a[j]=0;  
            }  
            a[i] = 0;  
        }  
    }  

    public static void main(String[] args)  
    {  
        int[] a = new int[9];         
        a[0] = 1;  

        for(int b=1; b<a.length; b++){  
            a[b] = 1;  
            for(int c=b+1; c<a.length; c++){  
                a[c] = 1;  
                String s = "A" + (char)(b+'A') + (char)(c+'A');  
                f(s,a);  
                a[c] = 0;  
            }  
            a[b] = 0;  
        }  
    }  
} 

  draw
        Planet X will send a five person observer mission to planet W.
        Among them:
        Country A can send up to four people.
        Country B can send up to two people.
        Country C can send up to two people.
        ....

        So how many different combinations of countries will the final mission to W star have?

        The following procedure solves this problem.
        Array a [] is the largest number of places that each country can send.
        The execution result of the program is:
        DEFFF
        CEFFF
        CDFFF
        CDEFF
        CCFFF
        CCEFF
        CCDFF
        CCDEF
        BEFFF
        BDFFF
        BDEFF
        BCFFF
        BCEFF
        BCDFF
        BCDEF
        ....
        (omitted below, 101 lines in total)

public class A  
    {  
        public static void f(int[] a, int k, int n, String s)  
        {  
            if(k==a.length){   
                if(n==0) System.out.println(s);  
                return;  
            }  

            String s2 = s;  
            for(int i=0; i<=a[k]; i++){  
                _____________________________;   //Fill in position  
                s2 += (char)(k+'A');  
            }  
        }  

        public static void main(String[] args)  
        {  
            int[] a = {4,2,2,1,1,3};  

            f(a,0,5,"");  
        }  
    }  

public class Main  
{  
    public static void f(int[] a, int k, int n, String s)  
    {  
        if(k==a.length){   
            if(n==0) System.out.println(s);  
            return;  
        }  

        String s2 = s;  
        for(int i=0; i<=a[k]; i++){  
            f(a,k+1,n-i,s2);   //Fill in position  
            s2 += (char)(k+'A');  
        }  
    }  

    public static void main(String[] args)  
    {  
        int[] a = {4,2,2,1,1,3};  

        f(a,0,5,"");  
       /* X The planet is going to send a five person observer mission to planet W.
        Among them:
        A The country can send up to four people.
        B The country can send up to two people.
        C The country can send up to two people.*/
    }  
}