Skip to main content

Insert node at first position in circular doubly link list

Now we will see how to insert a new node at first position in circular doubly link list.

Algorithm for insertion at first position in circular doubly link list:

In this algorithm, START is pointer to first node and PTR is node to be inserted. The step are as follows:
  • Create new node PTR
  • Set the info field of PTR
  • If list is empty i.e. START == NULL
    • Set START = PTR
    • Set PTR->NEXT = PTR
    • Set PTR->PREV = PTR
  • Else
    • Set PTR->NEXT = START
    • Set PTR->PREV = START->PREV
    • Set START->PREV->NEXT = PTR
    • Set START->PREV = PTR
    • Set START = PTR
  • End If;

Function to insert node at first position in circular doubly link list:


void insertAtFirst(NODE **start, int info){
 NODE *ptr = (NODE*) malloc(sizeof(NODE)); //new node to insert
 ptr->info = info; //set info field
 if(*start == NULL){ //empty list
  *start = ptr;
  ptr->next = ptr;
  ptr->prev = ptr;
 }
 else{
  ptr->next = *start; //ptr's next points to first node
  ptr->prev = (*start)->prev; // ptr's prev points to last node
  (*start)->prev->next = ptr; //last node's next point to ptr
  (*start)->prev = ptr; //first node's prev points to ptr
  *start = ptr; //now ptr is first node
 }
}

Program to insert at first position in the circular doubly link list:


#include <stdio.h>
#include <malloc.h>

typedef struct node{
 struct node *prev;
 int info;
 struct node *next;
} NODE;

void insertAtFirst(NODE **, int);
void traverse(NODE **);

int main(){
 NODE *start = NULL;
 insertAtFirst(&start, 3);
 insertAtFirst(&start, 24);
 insertAtFirst(&start, 4);
 traverse(&start);
 return 0;
}

void insertAtFirst(NODE **start, int info){
 NODE *ptr = (NODE*) malloc(sizeof(NODE)); //new node to insert
 ptr->info = info; //set info field
 if(*start == NULL){ //empty list
  *start = ptr;
  ptr->next = ptr;
  ptr->prev = ptr;
 }
 else{
  ptr->next = *start; //ptr's next points to first node
  ptr->prev = (*start)->prev; // ptr's prev points to last node
  (*start)->prev->next = ptr; //last node's next point to ptr
  (*start)->prev = ptr; //first node's prev points to ptr
  *start = ptr; //now ptr is first node
 }
}

void traverse(NODE **start){
 NODE *ptr = *start;
 if(ptr == NULL){
  printf("\nEmpty list\n");
  return;
 }
 while( ptr->next != *start ){
  printf("%d  ",ptr->info);
  ptr = ptr->next;
 }
 printf("%d\n",ptr->info);
}



4  24  3
 

Related topics:

Labels:

Comments

Post a Comment

Popular posts from this blog

Insertion at specific position N in singly link list

Insertion of a new node at position N in singly link list requires traversing the list for N-1 th node so that links are updated to accommodate the new node in the list. The new node's next is set to point to Nth node of the list and then N-1 th node's next pointer is updated so that it reference to new node. The step by step algorithm to insert node at Nth position is as below: Algorithm to insert node at specific position N in singly link list: This algorithm will insert the new node PTR at the position N in the link list. The steps are as follows: Create new node PTR Set the INFO field of PTR If N is less than 1 Node can't be inserted Else If node is to be inserted at first i.e. [N=1] Make new node PTR points to first node i.e. [PTR->NEXT = START] Make START point to new node PTR i.e. [START = PTR] Else Traverse the list to get the (N-1)th node of list into TEMP Make PTR's next pointer point to Nth node in the list i.e. [PTR -> NEXT  =  TEMP-...
Post a Comment
Read more

Prefix to Infix Conversion

With a given Prefix Expression, we will see how to convert Prefix Expression into Infix Expression using stack.   Algorithm to convert Prefix Expression to Infix Expression: In this algorithm, we will use stack to store operands during the conversion. The step are as follows: Read the prefix string While the end of prefix string scanned from right to left symb = the current character If symb is an operator poped_sym1 = pop the stack poped_sym2 = pop the stack concat the string  STR = ( poped_sym1 )+ ( operator )+( poped_sym2 ) push the string STR into stack Else push the operand symb into stack End If End While infix_str = pop the stack   Function to convert Prefix Expression to Infix Expression: void prefix_to_infix(char prefix[], char infix[]){ char op[2]; //operator string char poped1[MAX]; char poped2[MAX]; char temp[MAX]; int i = strlen(prefix); op[1] = '\0'; while(--i != -1){ if(prefix[i] == ' '){ continue; } if(isoper...
Post a Comment
Read more

Link List

In computer science, a linked list is a linear collection of elements, called nodes, each node have info field and next field pointing to the next node by means of a pointer. It is a data structure consisting of a group of nodes in sequence and connected with links. In simplest form of this data structure, each node is consist of data and a reference (in other words, a link) to the next node in the sequence. This structure allows for efficient insertion or removal of elements from any position in the sequence during iteration. Types of Link List Singly Link List: Insert node at first position in singly link list Insert node at last position in singly link list Insert node at specific position in singly link list Delete node at first position in singly link list Delete node at last position in singly link list Delete node at specific position in singly link list Find number of nodes in singly link list Dublication of singly link list Concatenation of two singly link list So...
Post a Comment
Read more