Question

Need help writing four short recursive programs:

1. Write a program called Permutations.java that takes an integer command-line argument, n, and enumerates all permutations of the first n letters in the English alphabet. Be sure to handle exceptions of the types: i) bad user input (i.e., double, string), ii) n > 26 or n < 0.

2. Write a program called PermutationsK.java that takes two integers, n and k, as command-line arguments and prints out all P(n,k) permutations that contain exactly k of the n elements. Note: P(n,k) = (n!)/(n-k)!

   1. Example: when n = 4, and k = 2: ab ac ad ba bc bd ca cb cd da db dc

   2. Be sure to handle the same exceptions as in (1).

3. Write a program called Combinations.java that takes an integer command line argument, n, and prints all 2n combinations of any size.

   1. Example: when n = 3: a ab abc ac b bc c (this should include the empty string)

   2. Be sure to handle the same exceptions as in (1).

4. Write a program called CombinationsK.java that makes two integers, n and k, as command-line arguments and prints all C(n,k) combinations of size k. Note: C(n,k) = (n!)/(k!(n-k)!)

   1. Example: when n = 5 and k = 3: abc abd abe acd ace ade bcd bce bde cde

   2. Be sure to handle the same exceptions as in (1).

Answer 1

Permuations.java

public class Permutations {

   public static void main(String[] args) {
       // TODO Auto-generated method stub
      
       String str;
      
       try {
       int n = Integer.parseInt(args[0]);
      
       if(n>0 && n<=26) {
          
           str = getStr(n);
          
          
           variations(str,0,n-1);
          
       }
      
       else
           System.out.println("Number should be between 1 and 26 Inclusive");
      
       }
       catch(NumberFormatException e) {
          
           System.out.println(e);
       }

      
      
      
   }
  
  
   public static String getStr(int n) {
      
       int i=0;
       String str = "";
       while(i<n) {
          
           str = str + (char)(i+65);
          
           i++;
       }
      
       return str;
   }
  
   public static void variations(String str, int m, int n)
{
if (m == n)
System.out.println(str);
else
{
for (int i = m; i <= n; i++)
{
str = mix(str,m,i);
variations(str, m+1, n);
str = mix(str,m,i);
}
}
}
  
   public static String mix(String a, int b, int c)
{
char dum;
char[] array = a.toCharArray();
dum = array[b] ;
array[b] = array[c];
array[c] = dum;
return String.valueOf(array);
}

}

When giving argument as HELLO

Out Put with exception

When Argument is given as 0

The output is

When Given an Valid input 10

Permutationsk.java

public class PermuationsK {

   public static void main(String[] args) {
       // TODO Auto-generated method stub
      
String str;
      
       try {
       int n = Integer.parseInt(args[0]);
       int k = Integer.parseInt(args[1]);
      
       if(n>0 && n<=26 && k>0 && k<=26 ) {
          
           if(n>=k) {
          
           str = getStr(n);
          
           // Calling the method
           printall(str,k);
          
           }
          
           else
               System.out.println("n value should be greater than or eaqual to k");
       }
      
       else
           System.out.println("Numbers should be between 1 and 26 Inclusive");
      
       }
       catch(NumberFormatException e) {
          
           System.out.println(e);
       }

   }
  
public static String getStr(int n) {
      
       int i=0;
       String str = "";
       while(i<n) {
          
           str = str + (char)(i+65);
          
           i++;
       }
      
       return str;
   }
  
public static void permutationsk(String str,String pre,int n, int k ,int k1,int count) {
  
   if(count<npr(n,k1)) {
   if (k == 0)
   {
      
   System.out.println(pre);
   return;
   }
  
     
   for (int i = 0; i < n; ++i)
   {
     
  
   String newPre = pre + str.charAt(i);
  
     
     
   permutationsk(str, newPre,
   n, k - 1,k1,count);
   count = count + 1;
  
     
   }
  
     
   }
  
   else
       return;
  
}
  
static void printall(String str, int k)
{
int n = str.length();
permutationsk(str, "", n, k,k,0);
}
  
public static int factorial(int n)
{
if (n <= 1)
return 1;
return n * factorial(n - 1);
}
  
public static int npr(int n, int r)
{
return factorial(n) / factorial(n - r);
}

}

When giving argument as Hi HELLO

OUTPUT is Like

When given 0output

OUTPUT IS LIKE

When n value is less than k value

OutPut is like

When the input is Valid

OUTPUT IS