Given two linked lists, insert nodes of the second list into the first list at alternate positions of the 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 the second list should only be inserted when there are positions available. For example, if the first list is 1->2->3 and the second list is 4->5->6->7->8, then the first list should become 1->4->2->5->3->6 and the 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. The expected time complexity is O(n) where n is a number of nodes in the 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.
<script> // Javascript program to merge a linked list // into another at alternate positions // A nexted list node class Node { constructor()
{
this .data = 0;
this .next = null ;
}
}; /* Function to insert a node at the beginning */
function push(head_ref, new_data)
{ var new_node = new Node();
new_node.data = new_data;
new_node.next = (head_ref);
(head_ref) = new_node;
return head_ref;
} /* Utility function to print a singly linked list */
function printList(head)
{ var temp = head;
while (temp != null )
{
document.write( temp.data + " " );
temp = temp.next;
}
document.write( "<br>" );
} // Main function that inserts nodes of // linked list q into p at alternate // positions. Since head of first list // never changes and head of second list // may change, we need single pointer for // first list and double pointer for second // list. function merge(p, q)
{ var p_curr = p, q_curr = q;
var p_next, q_next;
// While there are available positions
// in p
while (p_curr != null &&
q_curr != null )
{
// Save next pointers
p_next = p_curr.next;
q_next = q_curr.next;
// Make q_curr as next of p_curr
// Change next pointer of q_curr
q_curr.next = p_next;
// Change next pointer of p_curr
p_curr.next = q_curr;
// Update current pointers for next
// iteration
p_curr = p_next;
q_curr = q_next;
}
// Update head pointer of second list
q = q_curr;
return q;
} // Driver code var p = null , q = null ;
p = push(p, 3); p = push(p, 2); p = push(p, 1); document.write( "First Linked List:<br>" );
printList(p); q = push(q, 8); q = push(q, 7); q = push(q, 6); q = push(q, 5); q = push(q, 4); document.write( "Second Linked List:<br>" );
printList(q); q = merge(p, q); document.write( "Modified First Linked List:<br>" );
printList(p); document.write( "Modified Second Linked List:<br>" );
printList(q); // This code is contributed by rrrtnx. </script> |
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(N)
Auxiliary Space: O(1)
Please refer complete article on Merge a linked list into another linked list at alternate positions for more details!