Circular Doubly Link List

Circular Doubly Link List is data structure which contains a list of node containing info part and links to the next and previous node. In CDLL, last node's next pointer points to the first node and first node's previous pointer points to last node of the list. This makes traversal in both direction of CDLL. Before going to discuss the operation on circular doubly link list, we will first see the basic structure of the data type and see how it could be represented in c programming. First we will see the how the node or element of circular doubly link list is represented. See the image below:

The component of circular doubly list node:

info : It contains the actual information
next : This field points to the next node in the list
prev : This field points to the previous node in the list

Now we see how the circular doubly link list is represented. See the image below:

The component of circular doubly link list are:

START pointer points to the first node of the list
NODE : Each node have info field, next pointer to point next NODE in the list and prev pointer to point previous node in the list
PREV of first node points to last node and NEXT of last node will points to first node

The above structure of node is represented as below:


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

Now we will see the different operations that can be performed on the circular doubly link list:

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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-...

Concatenating two link list

Here we will see how to concat two single link list into other link list. First we copy the content of first list in third list and then the content of second list into third list. Algorithm for concatenation of two link list: This algorithm will use three list. List 1 and List 2 will be concatenated into List 3. The step below: Copy the list 1 into list 3 Copy the list 2 at the last of list 3 Function to concat two link list: void concatLists(NODE **start1, NODE **start2, NODE **mergeinto){ NODE *temp; temp = *start1; while(temp != NULL){ insertAtLast(&*mergeinto, temp->info); temp = temp->next; } temp = *start2; while(temp != NULL){ insertAtLast(&*mergeinto, temp->info); temp = temp->next; } } Program to concat two link lists: #include <stdio.h> #include <malloc.h> struct node{ int info; struct node *next; }; typedef struct node NODE; void insertAtLast(NODE **, int); void traverse(NODE **); void concatLists(NODE **,...

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...

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