C++ Program To Merge A Linked List Into Another Linked List At Alternate Positions
Given two linked lists, insert nodes of second list into first list at alternate positions of first list.
For example, if first list is 5->7->17->13->11 and second is 12->10->2->4->6, the first list should become 5->12->7->10->17->2->13->4->11->6 and second list should become empty. The nodes of second list should only be inserted when there are positions available. For example, if the first list is 1->2->3 and second list is 4->5->6->7->8, then first list should become 1->4->2->5->3->6 and second list to 7->8.
Use of extra space is not allowed (Not allowed to create additional nodes), i.e., insertion must be done in-place. Expected time complexity is O(n) where n is number of nodes in first list.
The idea is to run a loop while there are available positions in first loop and insert nodes of second list by changing pointers. Following are implementations of this approach.
C++
#include <bits/stdc++.h>
using namespace std;
class Node
{
public :
int data;
Node *next;
};
void push(Node ** head_ref,
int new_data)
{
Node* new_node = new Node();
new_node->data = new_data;
new_node->next = (*head_ref);
(*head_ref) = new_node;
}
void printList(Node *head)
{
Node *temp = head;
while (temp != NULL)
{
cout << temp -> data << " " ;
temp = temp -> next;
}
cout << endl;
}
void merge(Node *p, Node **q)
{
Node *p_curr = p, *q_curr = *q;
Node *p_next, *q_next;
while (p_curr != NULL &&
q_curr != NULL)
{
p_next = p_curr->next;
q_next = q_curr->next;
q_curr->next = p_next;
p_curr->next = q_curr;
p_curr = p_next;
q_curr = q_next;
}
*q = q_curr;
}
int main()
{
Node *p = NULL, *q = NULL;
push(&p, 3);
push(&p, 2);
push(&p, 1);
cout << "First Linked List:" ;
printList(p);
push(&q, 8);
push(&q, 7);
push(&q, 6);
push(&q, 5);
push(&q, 4);
cout << "Second Linked List:" ;
printList(q);
merge(p, &q);
cout <<
"Modified First Linked List:" ;
printList(p);
cout <<
"Modified Second Linked List:" ;
printList(q);
return 0;
}
|
Output:
First Linked List:
1 2 3
Second Linked List:
4 5 6 7 8
Modified First Linked List:
1 4 2 5 3 6
Modified Second Linked List:
7 8
Time Complexity: O(min(n1, n2)), where n1 and n2 represents the length of the given two linked lists.
Auxiliary Space: O(1), no extra space is required, so it is a constant.
Please refer complete article on Merge a linked list into another linked list at alternate positions for more details!
Last Updated :
16 Jun, 2022
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