Insert New Node Before Given Node in Linked List
In order to insert a new node before a given node in the linked list we have to follows the below steps:
(1) First we have to check weather free node is available in the Availability Stack or not. If free node is available then we can allocate memory to new node.
(2) After creating new node we have to check weather linked list is empty or not. We have two possibilities:
(A) Linked List is empty (FIRST=NULL). Hence list is empty, specified node is not found in the linked list. In this case we can not insert new node before given node.
(B) Linked List is not empty (FIRST ≠ NULL). In this case we have to traverse from first node to last node in the list until given node is found. If node is found in the linked list then we can insert new node before that node otherwise we can not insert new node before given node.
Algorithm to Insert New Node Before Given Node
Step 1: If AVAIL=NULL then
Write “Availability Stack is Empty”
Else
NEW_NODE=AVAIL
AVAIL = AVAIL->LINK
Step 2: If FIRST = NULL then
Write “Specified Node Not Found”
Else
NEW_NODE -> INFO = VALUE
SAVE = FIRST
Repeat while X ≠ SAVE->INFO and SAVE->LINK ≠ NULL
PRED = SAVE
SAVE = SAVE->LINK
If X = SAVE->INFO then
PRED->LINK= NEW_NODE
NEW_NODE->LINK=SAVE
Else
Write “Specified Node Not Found”
Step 3: Exit
Program to Insert New Node Before Given Node
#include<stdio.h>
#include<conio.h>
#include<alloc.h>
struct node
{
int info;
struct node *link;
};
struct node *FIRST;
void createlist()
{
char ch;
printf("Enter n for break\n");
ch=getchar();
while(ch!='n')
{
struct node *NEW_NODE,*SAVE;int x;
NEW_NODE=(struct node *)malloc(sizeof(struct node));
printf("Enter Data:");
scanf("%d",&x);
NEW_NODE->info=x;
if(FIRST==NULL)
{
NEW_NODE->link=NULL;
FIRST=NEW_NODE;
}
else
{
SAVE=FIRST;
while(SAVE->link!=NULL)
{
SAVE=SAVE->link;
}
SAVE->link=NEW_NODE;
NEW_NODE->link=NULL;
}
fflush(stdin);
printf("Enter n for break\n");
ch=getchar();
}
}
void insertbefore(int x)
{
struct node *NEW_NODE,*SAVE,*PRED;
int value;
NEW_NODE=(struct node *)malloc(sizeof(struct node));
printf("Enter value of node:");
scanf("%d",&value);
NEW_NODE->info=value;
if(FIRST==NULL)
{
printf("Specified Node Not Found\n");
}
else
{
SAVE=FIRST;
while(x!=SAVE->info && SAVE->link!=NULL)
{
PRED=SAVE;
SAVE=SAVE->link;
}
if(SAVE->info==x)
{
if(FIRST==SAVE)
{
NEW_NODE->link=SAVE;
FIRST=NEW_NODE;
}
else
{
NEW_NODE->link=SAVE;
PRED->link=NEW_NODE;
}
}
else
{
printf("Specified Node Not Found");
}
}
}
void display()
{
struct node *SAVE;
if(FIRST==NULL)
{
printf("Linked List is empty\n");
return;
}
printf("elements are:\n");
SAVE=FIRST;
while(SAVE!=NULL)
{
if(SAVE->link==NULL)
printf("|%d|",SAVE->info);
else
printf("|%d|->",SAVE->info);
SAVE=SAVE->link;
}
printf("\n");
return;
}
void main()
{
int x;
clrscr();
FIRST=NULL;
createlist();
display();
printf("Enter value of Node before which you want to enter new node:");
scanf("%d",&x);
insertbefore(x);
display();
getch();
}