代码
/*
* @lc app=leetcode.cn id=143 lang=cpp
*
* [143] 重排链表
*/
// @lc code=start
/**
* 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:
void reorderList(ListNode* head) {
if (!head) return;
int n = 0;
for (auto p = head; p; p = p->next) n++;
auto mid = head;
for (int i = 0; i < (n + 1) / 2 - 1; ++i) mid = mid->next;
auto a = mid, b = a->next;
for (int i = 0; i < n / 2; ++i) {
auto c = b->next;
b->next = a, a = b, b = c;
}
auto p = head, q = a;
for (int i = 0 ; i < n / 2; ++i) {
auto o = q->next;
q->next = p->next;
p->next = q;
if (n % 2 == 0 && i == n / 2 - 1) q->next = NULL;
p = q->next;
q = o;
}
if (n % 2) p->next = NULL;
}
};
// @lc code=end
