328. Odd Even Linked List

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {
        if(head == NULL || head->next == NULL || head->next->next == NULL) return head;
        ListNode* oddDummy = new ListNode(0);        //为了方便写while循环，这里设置两个头结点
        ListNode* evenDummy = new ListNode(0);
        ListNode* oddList = oddDummy;
        ListNode* evenList = evenDummy;
        int i = 1;
        while(head != NULL){
            if(i % 2 == 1){
                oddList->next = head;
                oddList = oddList->next;
            }else{
                evenList->next = head;
                evenList = evenList->next;
            }
            i++;
            ListNode* tmp = head->next;
            head->next = NULL;
            head = tmp;
        }
        oddList->next = evenDummy->next;
        return oddDummy->next;
    }
};