328 奇偶链表

https://leetcode.cn/leetbook/read/top-interview-questions-medium/xvdwtj/

cost: 47m46s

/**
 * 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) {}
 * };
 */
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {
        if (head == nullptr || head->next == nullptr) {
            return head;
        }
        auto p1 = head;
        auto p2 = head->next;
        auto head2 = p2;
        auto p = p2->next;
        while (p != nullptr) {
            p1->next = p;
            p1 = p1->next;
            p = p->next;
            if (p == nullptr) {
                break;
            }
            p2->next = p;
            p2 = p2->next;
            p = p->next;
        }
        p2->next = nullptr;
        p1->next = head2;
        return head;
    }
};