Linked List 10 operations from which problems are made ( complete guide for you)

/*
These are the functions we will implement make your seatbelts tight and start progrmming
cout<<" 1. Insert node at begining"<<endl;
cout<<" 2. Append a node"<<endl;
cout<<" 3. display the l.l"<<endl;
cout<<" 4. Insert before a selected node"<<endl;
cout<<" 5. Insert after a selected node "<<endl;
cout<<" 6.Delete a particular node"<<endl;
cout<<" 7.Reverse A L.L "<<endl;
cout<<" 8. Do bot reverse the l.l but display the reversed order (using recursion)"<<endl;
cout<<"9. find middle element in a list using slow and fast pointer"<<endl;
cout<<"10. check if linked list is palindrome or not (we know if even f=NULL odd f->next=NULL)"<<endl;
cout<<" 11. exit"<<endl;

*/


#include<iostream>
using namespace std;
struct node{
int data;
node* next;
};

void insertb(int d,node **h)
{
node* temp= new node();
temp->data=d;
temp->next=(*h);
*h=temp;
}
void display(node* h)
{
node* temp= (h);
while(temp!=NULL)
{


cout<<temp->data<<" ";
temp=temp->next;
}
}

void append(int d, node** h)
{
if((*h)==NULL)
{
*h= new node();
(*h)->data=d;
(*h)->next=NULL;
return;
}

node* temp = (*h);

while(temp->next!=NULL)
{
temp=temp->next;
}
node* temp2 = new node();
temp2->data=d;
temp2->next=NULL;
temp->next=temp2;

}
void reverse(node** h)
{
node * curr=(*h);
node *prev=NULL, *next=NULL;
while(curr!=NULL)
{
next=curr->next;
curr->next=prev;
prev=curr;
curr=next;
}
(*h)=prev;
}
void insertbefore(int d,int dd,node** h)
{
node *temp = new node();
temp->data=d;
node *curr=(*h);
node *prev=NULL;
while(curr->data!=dd)
{
prev=curr;
curr=curr->next;
}
temp->next=curr;
prev->next=temp;
}
void Deletewithdata(int d,node** h)
{
if((*h)==NULL) // if no element in l.l
{
return;
}
if((*h)->next==NULL) // if there is only one node
{
if((*h)->data==d) //  and that node is to be deleted
{
(*h)=(*h)->next;
return;
}
// one node is not matched
// cout<<" data is not in l.l"<<endl;
return;

}

node * prev=NULL;
node *curr=(*h);
while(curr!=NULL && curr->data!=d)
{
prev=curr;
curr=curr->next;
}
if(curr==NULL)
{
//cout<<" data is not in l.l"<<endl;
return;
}
prev->next=curr->next;
curr->next=NULL;

return;

}
void insertafter(int d,int dd,node** h)
{
node *temp= new node();
temp->data=d;
node *curr=(*h);
node *next=NULL;
while(curr->data!=dd)
{

curr=curr->next;
next=curr->next;
}
temp->next=next;
curr->next=temp;
}
void reverseList(node *head)
{
if(head==NULL)
{
return;
}
reverseList(head->next); // reverse l.l of next link first
cout<<head->data<<" ";

}
void findmiddle(node *head)
{
node *s=head;
node *f=head;
node *prevs=head;
while(f&&f->next&&s)
{

f=f->next->next;
prevs=s; // 2nd middle if even (i.e the first middle from left)
s=s->next;
}
cout<<s->data<<endl;

}
bool checkpalindrome(node *head)
{
// Algo go to middle and reverse either first half or second half and compare if ele are equal simple
//if we dont want to change the order  we will reverse again the ll  again
// we can also check this by using a vector or a stack but if they say to do it without using extra space this is approach

// let's reverse the later part of middle

// go to middle
node *f=head;
node *s=head;
node *prevs=head;
node * hh=head;
while(f&&f->next)
{
f=f->next->next;
prevs=s;
s=s->next;
}
if(f==NULL)//  if even then reverse from middle
{ node *prev=NULL;
node* next=s;
while(s!=NULL)
{
next=s->next;
s->next=prev;
prev=s;
s=next;
}
prevs->next=prev;
while(prev!=NULL)
{
if(prev->data!=hh->data)
return false;
}
return true;
}
else //odd if odd then reverse without involving middle
{node * ss= s->next;
node* next=ss;
node* prev=NULL;
while(ss!=NULL)
{
next=ss->next;
ss->next=prev;
prev=ss;
ss=next;
}
prevs->next->next=prev;
while(prev!=NULL)
{
if(prev->data!=hh->data)
return false;
}
return true;
}
}
int main()
{
cout<<" 1. Insert node at begining"<<endl;
cout<<" 2. Append a node"<<endl;
cout<<" 3. display the l.l"<<endl;
cout<<" 4. Insert before a selected node"<<endl;
cout<<" 5. Insert after a selected node "<<endl;
cout<<" 6.Delete a particular node"<<endl;
cout<<" 7.Reverse A L.L "<<endl;
cout<<" 8. Do bot reverse the l.l but display the reversed order (using recursion)"<<endl;
cout<<"9. find middle element in a list using slow and fast pointer"<<endl;
cout<<"10. check if linked list is palindrome or not (we know if even f=NULL odd f->next=NULL)"<<endl;
cout<<" 11. exit"<<endl;
//
//after a selected node 

int n,d,dd;

node* head=NULL;

while(1)
{
 cin>>n;
switch(n)
{
case 1:


cin>>d;
insertb(d,&head);

// see we are not returning any node since we are modifing by adderss in fun we use**
// itll be modified in list
// we'll modify the head as new inserted element
break;
case 2:
//append
cin>>d;
append(d,&head);
break;
case 3:
display(head);
break;
case 4:
cout<<" enter the data to enter \n";
cin>>d;
cout<<" enter the data before which "<<d<<"should be added"<<endl;
cin>>dd;
insertbefore(d,dd,&head);
break;
case 5:
cout<<" enter the data to enter \n";
cin>>d;
cout<<" enter the data after which "<<d<<"should be added"<<endl;
cin>>dd;
insertafter(d,dd,&head);
break;
case 6:
cout<<" enter the data to be deleted \n";
cin>>d;
Deletewithdata(d,&head);
break;
case 7:
reverse(&head);
break;
case 8:
reverseList(head); // not sending & as we just have to print
break;
case 9:
findmiddle(head); // not sending & as we just have to print
break;
case 10:
cout<<checkpalindrome(head)<<endl; // not sending & as we just have to print
break;
default:
break;
}
}

}