In this programming assignment, you will use linked lists to represent strings. You will implement functions that manipulate these linked lists to transmute the strings they represent. In doing so, you will master the craft of linked list manipulation!

For your linked lists, you must use the structs we have specified in ListyString.h without any modifications. You must #include this header file from ListyString.c like so:

#include "ListyString.h" The node struct you will use for your linked lists is defined in ListyString.h as follows:

typedef struct ListyNode {

char data; // Each node holds a single character.

struct ListyNode *next; // Pointer to next node in linked list.

} ListyNode;

Additionally, there is a ListyString struct that you will use to store the head of each linked list string, along with the length of that list:

typedef struct ListyString

{ struct ListyNode *head; // Pointer to head of string's linked list.

int length; // Length of this string / linked list.

 } ListyString; 

Command	Description
@ key str	In your working string, replace all instances of key with str.
+ str	Concatenate str to the end of your working string.
- key	Delete all instances of key (if any) from your working string.
~	Reverse the working string.
?	Print the number of characters in the working string.
!	Print the working string.

int main(int argc, char **argv);

Description: You have to write a main() function for this program. It should only do the following three things: (1) capture the name of an input file (passed as a command line argument), (2) call the processInputFile() function (passing it the name of the input file to be processed), and (3) return zero.

Returns: 0 (zero).

int processInputFile(char *filename);

Description: Read and process the input file (whose name is specified by the string filename) according to the description above in Section 2, Input Files. To perform the string manipulations described in that section, you should call the corresponding required functions listed below. In the event that a bad filename is passed to this function (i.e., the specified file does not exist), this function should simply return 1 without producing any output.

Output: This function should only produce output if the input file has ? and/or ! commands. For details, see Section 2 (Input Files), or refer to the input/output files included with this assignment. Note that this function should not produce any output if the input file does not exist.

Returns: If the specified input file does not exist, return 1. Otherwise, return 0.

ListyString *createListyString(char *str);

Description: Convert str to a ListyString by first dynamically allocating a new ListyString struct, and then converting str to a linked list string whose head node will be stored inside that ListyString struct. Be sure to update the length member of your new ListyString, as well.

Special Considerations: str may contain any number of characters, and it may contain non- alphanumeric characters. If str is NULL or an empty string (), simply return a new

ListyString whose head is initialized to NULL and whose length is initialized to zero. Runtime Requirement: This should be an O(k) function, where k is the length of str.

Returns: A pointer to the new ListyString. Ideally, this function would return NULL if any calls to malloc() failed, but I do not intend to test your code in an environment where malloc() would fail, so you are not required to check whether malloc() returns NULL.

ListyString *destroyListyString(ListyString *listy); 

Description: Free any dynamically allocated memory associated with the ListyString and return NULL. Be sure to avoid segmentation faults in the event that listy or listy->head are NULL.

Returns: NULL.

ListyString *cloneListyString(ListyString *listy);

Description: Using dynamic memory allocation, create and return a new copy of listy. Note that you should create an entirely new copy of the linked list contained within listy. (That is, you should not just set your new ListyStrings head pointer equal to listyhead.) The exception here is that if listy->head is equal to NULL, you should indeed create a new ListyStruct whose head member is initialized to NULL and whose length member is initialized to zero. If listy is NULL, this function should simply return NULL.

Runtime Requirement: The runtime of this function should be no worse than O(n), where n is the length of the ListyString.

Returns: A pointer to the new ListyString. If the listy pointer passed to this function is NULL, simply return NULL.

void replaceChar(ListyString *listy, char key, char *str); 

Description: This function takes a ListyString (listy) and replaces all instances of a certain character (key) with the specified string (str). If str is NULL or the empty string (), this function simply removes all instances of key from the linked list. If key does not occur anywhere in the linked list, the list remains unchanged. If listy is NULL, or if listy->head is NULL, simply return.

Important Note: Be sure to update the length member of the ListyString as appropriate.

Runtime Requirement: The runtime of this function should be no worse than O(n + km), where n is the length of the ListyString, k is the number of times key occurs in the ListyString, and m is the length of str.

Returns: Nothing. This is a void function.

void reverseListyString(ListyString *listy);

Description: Reverse the linked list contained within listy. Be careful to guard against

segfaults in the cases where listy is NULL or listy->head is NULL.

Runtime Consideration: Ideally, this function should be O(n), where n is the length of the ListyString. Note that if you repeatedly remove the head of listys linked list and insert it at the tail of a new linked list using a slow tail insertion function, that could devolve into an O(n2) approach to solving this problem.

Returns: Nothing. This is a void function.

ListyString *listyCat(ListyString *listy, char *str);

Description: Concatenate str to the end of the linked list string inside listy. If str is either NULL or the empty string (), then listy should remain unchanged. Be sure to update the length member of listy as appropriate.

Special Considerations: If listy is NULL and str is a non-empty string, then this function should create a new ListyString that represents the string str. If listy is NULL and str is NULL, this function should simply return NULL. If listy is NULL and str is a non-NULL empty string (), then this function should return a ListyString whose head member has been initialized to NULL and whose length member has been initialized to zero.

Runtime Requirement: The runtime of this function must be no worse than O(n+m), where n is the length of listy and m is the length of str.

Returns: If this function caused the creation of a new ListyString, return a pointer to that new ListyString. If one of the special considerations above requires that a NULL pointer be returned, then do so. Otherwise, return listy.

int listyCmp(ListyString *listy1, ListyString *listy2); 

Description: Compare the two ListyStrings. Return 0 (zero) if they represent equivalent strings. Otherwise, return any non-zero integer of your choosing. Note that the following are not considered equivalent: (1) a NULL ListyString pointer and (2) a non-NULL ListyString pointer in which the head member is set to NULL (or, equivalently, the length member is set to zero). For the purposes of this particular function, (2) represents an empty string, but (1) does not. Two NULL pointers are considered equivalent, and two empty strings are considered equivalent, but a NULL pointer is not equivalent to an empty string.

Runtime Requirement: The runtime of this function must be no worse than O(n+m), where n is the length of listy1 and m is the length of listy2.

Returns: 0 (zero) if the ListyStrings represent equivalent strings; otherwise, return any integer other than zero.

int listyLength(ListyString *listy); 

Description: Return the length of the ListyString (i.e., the length of listys linked list).

Runtime Requirement: The runtime of this function must be O(1).

Returns: The length of the string (i.e., the length of the linked list contained within listy). If listy is NULL, return -1. If listy is non-NULL, but listy->head is NULL, return zero.

void printListyString(ListyString *listy); 

Description: Print the string stored in listy, followed by a newline character, . If listy is NULL, or if listy represents an empty string, simply print (empty string) (without the quotes), follow by a newline character, .

Returns: Nothing. This is a void function.