LINKED LIST -- INSERT A NODE AT A PARTICULAR POSITION

 

LINKED LIST -- INSERT A NODE AT A PARTICULAR POSITION

Given the pointer to the head node of a linked list and an integer to insert at a certain position, create a new node with the given integer as its  attribute, insert this node at the desired position and return the head node.

A position of 0 indicates head, a position of 1 indicates one node away from the head and so on. The head pointer given may be null meaning that the initial list is empty.

Example
 refers to the first node in the list 

Insert a node at position  with . The new list is 

Function Description Complete the function insertNodeAtPosition in the editor below. It must return a reference to the head node of your finished list.

insertNodeAtPosition has the following parameters:

• head: a SinglyLinkedListNode pointer to the head of the list
• data: an integer value to insert as data in your new node
• position: an integer position to insert the new node, zero based indexing

Returns

• SinglyLinkedListNode pointer: a reference to the head of the revised list

Input Format

The first line contains an integer , the number of elements in the linked list.
Each of the next  lines contains an integer SinglyLinkedListNode[i].data.
The next line contains an integer , the data of the node that is to be inserted.
The last line contains an integer .

Constraints

• , where  is the  element of the linked list.
• .

Sample Input

3
16
13
7
1
2

Sample Output

16 13 1 7

Explanation

The initial linked list is . Insert  at the position  which currently has  in it. The updated linked list is  16 --> 13 --> 1 --> 7.

SOLUTION

SinglyLinkedListNode* insertNodeAtPosition(SinglyLinkedListNode* llist, int data, int position) {

    SinglyLinkedListNode* newnode=malloc(sizeof(SinglyLinkedList));

    SinglyLinkedListNode* insert=malloc(sizeof(SinglyLinkedList));

    insert->data=data;

    newnode=llist;

    if(llist==NULL){

        insert->next=NULL;

        llist=insert;

    }

    else{

    for (int i=0; i<=position; i++) {

        if(i==position-1){

            insert->next=newnode->next;

            newnode->next=insert;

        }

        else{

        //newnode->prev=newnode;

        newnode=newnode->next;

        }

    }

    }

    return llist;

}

int main()

{

    FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w");

    SinglyLinkedList* llist = malloc(sizeof(SinglyLinkedList));

    llist->head = NULL;

    llist->tail = NULL;

    char* llist_count_endptr;

    char* llist_count_str = readline();

    int llist_count = strtol(llist_count_str, &llist_count_endptr, 10);

    if (llist_count_endptr == llist_count_str || *llist_count_endptr != '\0') { exit(EXIT_FAILURE); }

    for (int i = 0; i < llist_count; i++) {

        char* llist_item_endptr;

        char* llist_item_str = readline();

        int llist_item = strtol(llist_item_str, &llist_item_endptr, 10);

        if (llist_item_endptr == llist_item_str || *llist_item_endptr != '\0') { exit(EXIT_FAILURE); }

        insert_node_into_singly_linked_list(&llist, llist_item);

    }

    char* data_endptr;

    char* data_str = readline();

    int data = strtol(data_str, &data_endptr, 10);

    if (data_endptr == data_str || *data_endptr != '\0') { exit(EXIT_FAILURE); }

    char* position_endptr;

    char* position_str = readline();

    int position = strtol(position_str, &position_endptr, 10);

    if (position_endptr == position_str || *position_endptr != '\0') { exit(EXIT_FAILURE); }

    SinglyLinkedListNode* llist_head = insertNodeAtPosition(llist->head, data, position);

    char *sep = " ";

    print_singly_linked_list(llist_head, sep, fptr);

    fprintf(fptr, "\n");

    free_singly_linked_list(llist_head);

    fclose(fptr);

    return 0;

}

char* readline() {

    size_t alloc_length = 1024;

    size_t data_length = 0;

    char* data = malloc(alloc_length);

    while (true) {

        char* cursor = data + data_length;

        char* line = fgets(cursor, alloc_length - data_length, stdin);

        if (!line) { break; }

        data_length += strlen(cursor);

        if (data_length < alloc_length - 1 || data[data_length - 1] == '\n') { break; }

        size_t new_length = alloc_length << 1;

        data = realloc(data, new_length);

        if (!data) { break; }

        alloc_length = new_length;

    }

    if (data[data_length - 1] == '\n') {

        data[data_length - 1] = '\0';

    }

    data = realloc(data, data_length);

    return data;

}