题目

recorder-list

算法

* 直接模拟

代码

* 快慢指针

class Solution {
public:
    void reorderList(ListNode *head) {
        if (!head || !head->next || !head->next->next) return;
        ListNode *fast = head;
        ListNode *slow = head;
        while (fast->next && fast->next->next) {
            slow = slow->next;
            fast = fast->next->next;
        }
        ListNode *mid = slow->next;
        slow->next = NULL;
        ListNode *last = mid;
        ListNode *pre = NULL;
        while (last) {
            ListNode *next = last->next;
            last->next = pre;
            pre = last;
            last = next;
        }
        while (head && pre) {
            ListNode *next = head->next;
            head->next = pre;
            pre = pre->next;
            head->next->next = next;
            head = next;
        }
    }
};