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9.c
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9.c
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/*
* Implement a function to check whether a linked list is palindrome or not.
*
* 1. Get middle node of the linked list.
* 2. Reverse the second half of the linked list.
* 3. Check if both halves are identical or not.
*/
#include <stdio.h>
#include <stdlib.h>
struct node{
int data;
struct node *next;
};
struct node *head = NULL;
struct node *tail = NULL;
struct node *middle = NULL;
struct node *head1 = NULL;
struct node *head2 = NULL;
void insert_begin(int n){
struct node *temp;
if(head == NULL){
temp = (struct node *)malloc(sizeof(struct node));
temp->data = n;
temp->next = NULL;
head = tail = temp;
}
else{
temp = (struct node *)malloc(sizeof(struct node));
temp->data = n;
temp->next = head;
head = temp;
}
}
void insert_end(int n){
struct node *temp;
if(head == NULL){
temp = (struct node *)malloc(sizeof(struct node));
temp->data = n;
temp->next = NULL;
head = tail = temp;
}
else{
temp = (struct node *)malloc(sizeof(struct node));
temp->data = n;
temp->next = NULL;
tail->next = temp;
tail = temp;
}
}
void delete_node(int n){
struct node *prev = NULL;
struct node *curr = head;
while(curr != NULL){
//Delete head.
if(prev == NULL && curr->data == n){
head = curr = curr->next;
}
else if(curr->data == n && prev != NULL){
prev->next = curr->next;
curr = curr->next;
}
else{
prev = curr;
curr = curr->next;
}
}
}
void print_list(){
struct node *temp = head;
while(temp != NULL){
printf("%d --> ", temp->data);
temp = temp->next;
}
printf("NULL\n");
}
void print_list_ref(struct node *temp){
while(temp != NULL){
printf("%d --> ", temp->data);
temp = temp->next;
}
printf("NULL\n");
}
int list_length(){
int count = 0;
struct node *temp = head;
while(temp != NULL){
count++;
temp = temp->next;
}
return count;
}
void reverse_list(struct node **temp){
struct node *prev = NULL;
struct node *curr = *temp;
struct node *next;
while(curr != NULL){
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
head2 = prev;
}
struct node * get_middle_node(int count){
int middle_count;
int loop = 0;
struct node *temp = head;
if(count%2 == 0)
middle_count = count/2;
else
middle_count = (count - 1)/2;
printf("count %d middle %d\n", count, middle_count);
while(loop != middle_count){
temp = temp->next;
loop++;
}
middle = temp;
return middle;
}
void compare_list(struct node *temp1, struct node *temp2){
int flag = 0;
while(temp1 != NULL || temp2 != NULL){
if(temp1->data == temp2->data)
{
temp1 = temp1->next;
temp2 = temp2->next;
flag++;
}
else
{
flag = 0;
break;
}
}
if(flag)
printf("The given linked list is a perfect palindrome\n");
else
printf("The give linked list is not a palindrome\n");
}
int main(int argc, char **argv){
int count, middle;
insert_end(1);
insert_end(2);
insert_end(3);
insert_end(4);
insert_end(3);
insert_end(2);
insert_end(1);
insert_end(4);
print_list();
count = list_length();
printf("Length of the given linked list is %d\n", count);
head1 = head;
struct node *middle_node = get_middle_node(count);
printf("Middle node is %d\n", middle_node->data);
reverse_list(&middle_node);
print_list_ref(head1);
print_list_ref(head2);
compare_list(head1, head2);
return 0;
}