Odd Even Linked List

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

/*
Logic:
break the linked list into two halves ,one for the odd position and one for even positions.
then join both of them.
*/
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {
        if(!head || !(head->next)) return head;
        ListNode *odd=NULL,*even=NULL;
        odd=head;
        even=head->next;
        ListNode *o=odd,*e=even;
        while(o || e){
            if(o->next && o->next->next){ o->next=o->next->next; o=o->next;}
            if(e->next && e->next->next){ e->next=e->next->next; e=e->next;}
            if(!e->next || !o->next) break;
        }
        e->next=NULL;
        o->next=even;
        return odd;
    }
};