# C Program For Rearranging A Linked List Such That All Even And Odd Positioned Nodes Are Together

Rearrange a linked list in such a way that all odd position nodes are together and all even positions node are together, **Examples:**

Input:1->2->3->4Output:1->3->2->4Input:10->22->30->43->56->70Output:10->30->56->22->43->70

The important thing in this question is to make sure that all below cases are handled

- Empty linked list.
- A linked list with only one node.
- A linked list with only two nodes.
- A linked list with an odd number of nodes.
- A linked list with an even number of nodes.

The below program maintains two pointers ‘odd’ and ‘even’ for current nodes at odd and even positions respectively. We also store the first node of the even linked list so that we can attach the even list at the end of the odd list after all odd and even nodes are connected together in two different lists.

## C

`// C program to rearrange a linked list in ` `// such a way that all odd positioned node ` `// are stored before all even positioned ` `// nodes` `#include<bits/stdc++.h>` `using` `namespace` `std;` ` ` `// Linked List Node` `struct` `Node` `{` ` ` `int` `data;` ` ` `struct` `Node* next;` `};` ` ` `// A utility function to create a ` `// new node` `Node* newNode(` `int` `key)` `{` ` ` `Node *temp = ` `new` `Node;` ` ` `temp->data = key;` ` ` `temp->next = NULL;` ` ` `return` `temp;` `}` ` ` `// Rearranges given linked list such that ` `// all even positioned nodes are before ` `// odd positioned. Returns new head of ` `// linked List.` `Node *rearrangeEvenOdd(Node *head)` `{` ` ` `// Corner case` ` ` `if` `(head == NULL)` ` ` `return` `NULL;` ` ` ` ` `// Initialize first nodes of even ` ` ` `// and odd lists` ` ` `Node *odd = head;` ` ` `Node *even = head->next;` ` ` ` ` `// Remember the first node of even ` ` ` `// list so that we can connect the ` ` ` `// even list at the end of odd list.` ` ` `Node *evenFirst = even;` ` ` ` ` `while` `(1)` ` ` `{` ` ` `// If there are no more nodes, then ` ` ` `// connect first node of even list ` ` ` `// to the last node of odd list` ` ` `if` `(!odd || !even || !(even->next))` ` ` `{` ` ` `odd->next = evenFirst;` ` ` `break` `;` ` ` `}` ` ` ` ` `// Connecting odd nodes` ` ` `odd->next = even->next;` ` ` `odd = even->next;` ` ` ` ` `// If there are NO more even ` ` ` `// nodes after current odd.` ` ` `if` `(odd->next == NULL)` ` ` `{` ` ` `even->next = NULL;` ` ` `odd->next = evenFirst;` ` ` `break` `;` ` ` `}` ` ` ` ` `// Connecting even nodes` ` ` `even->next = odd->next;` ` ` `even = odd->next;` ` ` `}` ` ` ` ` `return` `head;` `}` ` ` `// A utility function to print a ` `// linked list` `void` `printlist(Node * node)` `{` ` ` `while` `(node != NULL)` ` ` `{` ` ` `cout << node->data << ` `"->"` `;` ` ` `node = node->next;` ` ` `}` ` ` `cout << ` `"NULL"` `<< endl;` `}` ` ` `// Driver code` `int` `main(` `void` `)` `{` ` ` `Node *head = newNode(1);` ` ` `head->next = newNode(2);` ` ` `head->next->next = newNode(3);` ` ` `head->next->next->next = newNode(4);` ` ` `head->next->next->next->next = newNode(5);` ` ` ` ` `cout << ` `"Given Linked List"` `;` ` ` `printlist(head);` ` ` ` ` `head = rearrangeEvenOdd(head);` ` ` ` ` `cout << ` `"Modified Linked List"` `;` ` ` `printlist(head);` ` ` ` ` `return` `0;` `}` |

**Output:**

Given Linked List 1->2->3->4->5->NULL Modified Linked List 1->3->5->2->4->NULL

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