https://leetcode.com/problems/odd-even-linked-list/

    1. //20 ms    8.4 MB
    3. /**
    4.  * Definition for singly-linked list.
    5.  * struct ListNode {
    6.  *     int val;
    7.  *     ListNode *next;
    8.  *     ListNode(int x) : val(x), next(NULL) {}
    9.  * };
    10.  */
    12. //CAUTION: it is talking about the node number and not the value in the nodes
    13. class Solution {
    14. public:
    15.     ListNode* oddEvenList(ListNode* head) {
    16.         if(!head || !head->next) return head;
    18.         ListNode* odd = head;
    19.         ListNode* even = head->next;
    20.         ListNode* head2 = even;
    22.         while(odd->next && even->next){
    23.             odd->next = even->next;
    24.             odd = odd->next;
    26.             even->next = odd->next;
    27.             even = even->next;
    28.         }
    29.         odd->next = head2;
    31.         return head;
    32.     }
    33. };