328. Odd Even Linked List , Medium
method 1
- could form separate LL and then merge them later.
optimal method
- instead of using extra space.
- we can play with
next address.
Code
```cpp
class Solution {
public:
ListNode* oddEvenList(ListNode* head) {
if (head == nullptr)
return head;
ListNode *even = head -> next;
ListNode *odd = head;
ListNode *evenHead = even;
while (even != nullptr and even -> next != nullptr) {
odd -> next = odd -> next -> next;
even -> next = even -> next -> next;
odd = odd -> next;
even = even -> next;
}
odd -> next = evenHead;
return head;
}
};
```