// =================== Support Code ================= // Doubly Linked List ( DLL ). // // // // - Implement each of the functions to create a working DLL. // - Do not change any of the function declarations // - (i.e. dll_t* create_dll() should not have additional arguments) // - You should not have any 'printf' statements in your DLL functions. // - (You may consider using these printf statements to debug, // but they should be removed from your final version) // - (You may write helper functions to help you debug your code such as print_list etc) // ================================================== #ifndef MYDLL_H #define MYDLL_H

// Create a node data structure to store data within // our DLL. In our case, we will stores 'integers' typedef struct node { int data; struct node* next; struct node* previous; } node_t;

// Create a DLL data structure // Our DLL holds a pointer to the first node in our DLL called head, // and a pointer to the last node in our DLL called tail. typedef struct DLL { int count; // count keeps track of how many items are in the DLL. node_t* head; // head points to the first node in our DLL. node_t * tail; //tail points to the last node in our DLL. } dll_t;

// Creates a DLL // Returns a pointer to a newly created DLL. // The DLL should be initialized with data on the heap. // (Think about what the means in terms of memory allocation) // The DLLs fields should also be initialized to default values. // Returns NULL if we could not allocate memory. dll_t* create_dll(){ // Modify the body of this function as needed. dll_t* myDLL= NULL;

// TODO: Implement me!! return myDLL; }

// DLL Empty // Check if the DLL is empty // Returns -1 if the dll is NULL. // Returns 1 if true (The DLL is completely empty) // Returns 0 if false (the DLL has at least one element enqueued) int dll_empty(dll_t* t){ // TODO: Implement me!! return -1; }

// push a new item to the front of the DLL ( before the first node in the list). // Returns -1 if DLL is NULL. // Returns 1 on success // Returns 0 on failure ( i.e. we couldn't allocate memory for the new node) // (i.e. the memory allocation for a new node failed). int dll_push_front(dll_t* t, int item){ // TODO: Implement me!! return -1; }

// push a new item to the end of the DLL (after the last node in the list). // Returns -1 if DLL is NULL. // Returns 1 on success // Returns 0 on failure ( i.e. we couldn't allocate memory for the new node) // (i.e. the memory allocation for a new node failed). int dll_push_back(dll_t* t, int item){ // TODO: Implement me!! return -1; }

// Returns the first item in the DLL and also removes it from the list. // Returns -1 if the DLL is NULL. // Returns 0 on failure, i.e. there is noting to pop from the list. // Assume no negative numbers in the list or the number zero. int dll_pop_front(dll_t* t){ // TODO: Implement me!! return -1; // Note: This line is a 'filler' so the code compiles. }

// Returns the last item in the DLL, and also removes it from the list. // Returns a -1 if the DLL is NULL. // Returns 0 on failure, i.e. there is noting to pop from the list. // Assume no negative numbers in the list or the number zero. int dll_pop_back(dll_t* t){ // TODO: Implement me!! return -1; // Note: This line is a 'filler' so the code compiles. }

// Inserts a new node before the node at the specified position. // Returns -1 if the list is NULL // Returns 1 on success // Retruns 0 on failure: // * we couldn't allocate memory for the new node // * we tried to insert at a negative location. // * we tried to insert past the size of the list // (inserting at the size should be equivalent as calling push_back). int dll_insert(dll_t* t, int pos, int item){ // TODO: Implement me!! return -1; // Note: This line is a 'filler' so the code compiles. }

// Returns the item at position pos starting at 0 ( 0 being the first item ) // Returns -1 if the list is NULL // (does not remove the item) // Returns 0 on failure: // * we tried to get at a negative location. // * we tried to get past the size of the list // Assume no negative numbers in the list or the number zero. int dll_get(dll_t* t, int pos){ // TODO: Implement me!! return -1; // Note: This line is a 'filler' so the code compiles. }

// Removes the item at position pos starting at 0 ( 0 being the first item ) // Returns -1 if the list is NULL // Returns 0 on failure: // * we tried to remove at a negative location. // * we tried to remove get past the size of the list // Assume no negative numbers in the list or the number zero. int dll_remove(dll_t* t, int pos){ // TODO: Implement me!! return -1; // Note: This line is a 'filler' so the code compiles. }

// DLL Size // Returns -1 if the DLL is NULL. // Queries the current size of a DLL int dll_size(dll_t* t){ // TODO: Implement me!! return -1; // Note: This line is a 'filler' so the code compiles. }

// Free DLL // Removes a DLL and all of its elements from memory. // This should be called before the proram terminates. void free_dll(dll_t* t){ // TODO: Implement me!! }

#endif