# Assignment #6 Solution

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## Description

(See the syllabus for late policy)

Objective: The goal of this assignment is to practice recursion.

Assignment: The assignment requires writing recursive methods for some linked list operations. The use of loops in the recursive methods is strictly prohibited in this assignment. That is, you cannot use for, while, and do-while in the recursive methods you will write. You can only use a loop when you will initiate values for a linked list in the main method. You will need to write a method to generate a random String. You can use loops in that method too.

Consider that you are given the following linked list node.

public class StringNode {

public StringNode next;

StringNode(){}

StringNode(String s){

}

StringNode(String s, StringNode tail){

next=tail;

}

}

Clearly, the StringNode class can be used to create a linked list. Write a class named Operations that will contain the methods described below. In addition, some instructions are given as comments of the partial code provided later in this assignment.

1. Write a method named getRandString(int length) that will return a String of length given in the parameter. This method need not be a recursive one. The returned String may only contain English letters in capital (that is, letters from A to Z).

2. Write a recursive method named printMyList(StringNode m) to print all the strings in the linked list m. Notice that m is the head of the linked list.

1. Write a recursive method named countKLenghthStrings (StringNode m, int k) that will return number of Strings with length k in the given linked list m.

1. Write a recursive method named longestStringOfMyList (StringNode m) that will return the longest String in a linked list.

2. Write a recursive method named lengthOfMyList (StringNode m) that will compute and return the length of a given linked list m.

1. Write a recursive method named StringNode reverseMyList (StringNode m) to reverse a linked list. Return the head of the reversed linked list.

2. Write a recursive method named

StringNode removeAStringFromMyList(StringNode m, String removee) to remove the first occurrence of removee from a given linked list m.

8. Write a recursive method named

StringNode insertAStringIntoMyList(StringNode m, String insertee, int position)

to insert a String (insertee) into a specific position of a given linked list m. Positions start from 0 (that is, the position of the head of a list is considered 0).

1. Write a recursive method named

boolean isListInOrder(StringNode m)

to verify if the strings in a linked list m are lexicographically ordered. Return true if they are ordered, false otherwise.

1. Write a recursive method named

int countPalindromes(StringNode m)

that will count how many strings of a given linked list are palindromes. The method must call another recursive method named

boolean isPalindrome(String s)

to verify if a String is a palindrome. Palindrome check must NOT be case-sensitive.

A template for the Operations class is given below. You need to write your codes inside the body of the methods provided with Operations. Modify the main method for testing purpose, as necessary. The comments in the Operations class provide detailed requirements.

public class Operations {

public static void main(String[] args){

StringNode L=new StringNode(“0”+getRandString(2+(int)(Math.random()*5))); StringNode temp = L;

for (int i=1; i<=9;i++){

temp.next=new StringNode(i+getRandString(2+(int)(Math.random()*5))); temp=temp.next;

}

System.out.println(“All Strings in the list:”); printMyList(L);

System.out.println();

boolean b = isListInOrder(L);

System.out.println(“List is ordered: “+b);

System.out.println();

System.out.println(“Count of k-length strings”); System.out.println(“k\tNo. of Strings with length k”); for (int k=0; k<7; k++){

System.out.println(k+\t+countKLenghthStrings(L, k));

}

System.out.println(“Longest String=”+longestStringOfMyList(L)); System.out.println(“Length=”+lengthOfMyList(L));

L=reverseMyList(L);

System.out.println(“All string in the reversed list:”); printMyList(L);

System.out.println();

System.out.println(“Remove a given String”);

System.out.println(“All strings in the new list:”); printMyList(LL);

System.out.println();

System.out.println(“All strings in the previous list:”); printMyList(L);

System.out.println();

System.out.println(“Insert a string in a position of the new list:”); LL=insertAStringIntoMyList(LL, “Hello world”, 3); printMyList(LL);

System.out.println();

b = isListInOrder(L);

System.out.println(“List is ordered: “+b);

System.out.println();

LL=insertAStringIntoMyList(LL, “ABBA”, 3);

LL=insertAStringIntoMyList(LL, “DoGeeseSeeGod”, 3);

int c = countPalindromes(LL);

System.out.println(“Found “+c+” palindromes.”);

}

static String getRandString(int length) {

/* Write your code here */

}

/* Write a recursive method to print all the strings in separate lines. This method cannot contain any loop (that is, uses of for, while, do while are prohibited).

*/

public static void printMyList(StringNode m){ /* Write your code here */

}

/* Write a recursive method to retrieve the number of strings that are longer than the length provided in the parameter. This method cannot contain any loop (that is, uses of for, while, do while are prohibited).

*/

public static int countKLenghthStrings (StringNode m, int k){ /* Write your code here */

}

/* Write a recursive method to retrieve the largest String from the list. Assume that there is at least one String in the given list when the method is called from the main function. This method cannot contain any loop (that is, uses of for, while, do while are prohibited).

*/

public static String longestStringOfMyList (StringNode m){ /* Write your code here */

}

/* Write a recursive method to compute the length of a list.

This method cannot contain any loop (that is, uses of for, while, do while are prohibited).

*/

public static int lengthOfMyList (StringNode m){ /* Write your code here */

}

/* Write a recursive method named reverseMyList that will reverse a given linked list m. Return the head of the reversed linked list. It is fine if you need to modify the given linked list to obtain the reversed one. */

public static StringNode reverseMyList (StringNode m){ /* Write your code here */

}

/* Write a recursive method to remove the first occurrence of a specific String from a list. As an example, if your list initially contains

1. BB CC DD BB KK and if your removee is BB, the returned list should contain AA CC DD BB KK after the removal. Return a new head. You must make sure that the parameter list m remains intact after returning the new list to the main method. This method cannot contain any loop (that is, uses of for, while, do-while are prohibited).

*/

public static StringNode removeAStringFromMyList(StringNode m, String removee){

/* Write your code here */

}

/* Write a recursive method to insert a String (insertee) into a specific position of a list. Positions start from 0 (that is, the position of the head of a list is 0). This method cannot contain any loop (that is, uses of for, while, do-while are prohibited). */

public static StringNode insertAStringIntoMyList(StringNode m, String insertee, int position){

/* Write your code here */

}

/* Write a recursive method to verify if the strings are lexicographically ordered in a linked list. Return true if they are ordered, false otherwise. This method cannot contain any loop (that is, uses of for, while, do-while are prohibited).

*/

public static boolean isListInOrder(StringNode m){ /* Write your code here */

}

/* Write a recursive method that will count how many strings of a given linked list are palindromes. The method must call another recursive method named isPalindrome to verify if a String is a palindrome, or

not. Palindrome checks must NOT be case-sensitive. Neither countPalindromes nor isPalindrome may contain loops (that is, uses of for, while, do-while are prohibited).

*/

public static int countPalindromes(StringNode m){ /* Write your code here */

}

public static boolean isPalindrome(String s){ /* Write your code here */

}

}

Output of the program above is as follows. Note that a part of each string is random and hence the output may change for a different execution.

All Strings in the list:

0WTR

1VUX

2VZ

3SUMHD

4FIEU

5JFW

6GAKBO

7XDOF

8XTCRPF

9LH

List is ordered: true

Count of k-length strings

k No. of Strings with length k

1. 0

2. 0

3. 0

4. 2

5. 3

6. 2

7. 2

Longest String=8XTCRPF

Length=10

All string in the reversed list:

9LH

8XTCRPF

7XDOF

6GAKBO

5JFW

4FIEU

3SUMHD

2VZ

1VUX

0WTR

Remove a given String

All strings in the new list:

9LH

8XTCRPF

6GAKBO

5JFW

4FIEU

3SUMHD

2VZ

1VUX

0WTR

All strings in the previous list:

9LH

8XTCRPF

7XDOF

6GAKBO

5JFW

4FIEU

3SUMHD

2VZ

1VUX

0WTR

Insert a string in a position of the new list:

9LH

8XTCRPF

6GAKBO

Hello world

5JFW

4FIEU

3SUMHD

2VZ

1VUX

0WTR

List is ordered: false

Palindrome:DoGeeseSeeGod

Palindrome:ABBA

Found 2 palindromes.

Any use of java.util.LinkedList is strictly prohibited.

Deliverables: You are expected to submit two Java files ( StringNode.java and Operations.java) via Blackboard. Your TA will instruct you with further details.

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