# Append Last N Nodes to First in the Linked List using C++ program

Here, we are going to learn how to append last N nodes to first in the linked list using a C++ program?
Submitted by Indrajeet Das, on December 19, 2018

Given a linked list and an integer n, append the last n elements of the LL to front. Assume given n will be smaller than length of LL.

Input format: Line 1: Linked list elements (separated by space and terminated by -1

```    Sample Input 1 :
1 2 3 4 5 -1
3

Sample Output 1 :
3 4 5 1 2
```

Description:

The question asks us to append the last N nodes to front, i.e the new linked list should first start from those N nodes and then traverse the rest of the nodes through the head of the old linked list.

Example:

```    For Linked List 1->2->3->4->5->6->NULL
To append the last 2 nodes, the new linked list should be:
5->6->1->2->3->4->NULL
```

Solution Explanation:

To solve this problem, we take two pointers temp and t and point both of them to the head of the linked list. We take another variable i and equate it to – n. This i is used for finding out the head of the new linked list. Then we traverse the loop while temp != NULL. In the loop we check that if(i>=0) i.e temp is now n nodes away from t, t = t-> next. We will update i++ and temp = temp->next on each traversal. At last, we update temp-> next = head, head = t -> next and t-> next = NULL.

Algorithm:

• STEP 1: Declare the function appendNNode with parameters (Node* head, int n)
• STEP 2: Declare two variables Node * temp , t and point both of them to head.
• STEP 3: Declare int i = -n
• STEP 4: Repeat Step 5 and 6, while(temp->next != NULL)
• STEP 5: if(i>=0) t = t-> next.
• STEP 6: temp = temp-> next, i++.
• STEP 7: temp->next = head, head = t->next, and t-> next =NULL

Steps:

```    At first: 1->2->3->4->5->6->NULL, t->1 and temp->1.
After complete traversal: 1->2->3->4->5->6->NULL, t->4 and temp->6.
i.e 5->6->1->2->3->4 --- (reconnecting to 5)
Atlast, t-> next = NULL
i.e 5->6->1->2->3->4->NULL
```

Function:

```Node *appendNNodes(Node* head, int n){
// Two pointers, one for traversal and
// other for finding the new head of LL
//index maintained for finding new head
int i = -n;
while(temp->next!=NULL){
//When temp went forward n nodes from t
if(i>=0){
t = t->next;
}
temp = temp ->next;
i++;
}
//Assigning the new node
//Deleting the previous connection
t->next = NULL;
}
```

C++ Code:

```#include<bits/stdc++.h>

using namespace std;

int data;
Node * next;
};

Node *newNode(int k){ //defining new node
Node *temp = (Node*)malloc(sizeof(Node));
temp->data = k;
temp->next = NULL;
return temp;
}

//Used to add new node at the end of the list
}
else{
Node * node = newNode(k);
while(temp->next!= NULL){
temp = temp->next;
}
temp-> next = node;
}

}

Node *createNewLL(){
int cont = 1;
int data;
while(cont){
cout<<"Enter the data of the Node"<<endl;
cin>>data;
cout<<"Do you want to continue?(0/1)"<<endl;
cin>>cont;
}
}

}
cout<<"NULL"<<endl;
}

//Function
// Two pointers, one for traversal and
// other for finding the new head of LL
//index maintained for finding new head
int i = -n;
while(temp->next!=NULL){
//When temp went forward n nodes from t
if(i>=0){
t = t->next;
}
temp = temp ->next;
i++;
}
//Assigning the new node
//Deleting the previous connection
t->next = NULL;

}

//Driver Main
int main(){
int data;
cout<<"Enter the number of nodes you want to append."<<endl;
cin>>data;
cout<<"The new Linked List is" <<endl;

return 0;
}
```

Output

```Enter the data of the Node
1
Do you want to continue?(0/1)
1
Enter the data of the Node
2
Do you want to continue?(0/1)
1
Enter the data of the Node
3
Do you want to continue?(0/1)
1
Enter the data of the Node
4
Do you want to continue?(0/1)
1
Enter the data of the Node
5
Do you want to continue?(0/1)
1
Enter the data of the Node
6
Do you want to continue?(0/1)
1
Enter the data of the Node
7
Do you want to continue?(0/1)
0
1->2->3->4->5->6->7->NULL
Enter the number of nodes you want to append.
3
5->6->7->1->2->3->4->NULL
```

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