NC207 排序奇升偶降链表
/**
* struct ListNode {
* int val;
* struct ListNode *next;
* ListNode(int x) : val(x), next(nullptr) {}
* };
*/
class Solution {
pair<ListNode *, ListNode *> splitOddEvenList(ListNode *head) {
if (!head)
return {nullptr, nullptr};
ListNode *dummyHead = new ListNode(0);
ListNode *prev1 = head;
ListNode *prev2 = dummyHead, *curr2 = head->next;
while (curr2) {
prev1->next = curr2->next;
prev2->next = curr2;
prev1 = prev1->next;
prev2 = curr2;
if (!prev1)
break;
curr2 = prev1->next;
}
prev2->next = nullptr;
ListNode *head2 = dummyHead->next;
delete dummyHead;
return {head, head2};
}
ListNode* reverseList(ListNode *head) {
ListNode *prev = nullptr, *curr = head, *next;
while (curr) {
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
return prev;
}
ListNode* mergeSortedList(ListNode *head1, ListNode *head2) {
ListNode *dummyHead = new ListNode(0), *prev = dummyHead;
ListNode *curr1 = head1, *curr2 = head2;
while (curr1 && curr2) {
if (curr1->val <= curr2->val) {
prev->next = curr1;
curr1 = curr1->next;
} else {
prev->next = curr2;
curr2 = curr2->next;
}
prev = prev->next;
}
while (curr1) {
prev->next = curr1;
curr1 = curr1->next;
prev = prev->next;
}
while (curr2) {
prev->next = curr2;
curr2 = curr2->next;
prev = prev->next;
}
ListNode *head = dummyHead->next;
delete dummyHead;
return head;
}
public:
/**
* 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可
*
*
* @param head ListNode类
* @return ListNode类
*/
ListNode* sortLinkedList(ListNode* head) {
auto [head1, head2] = splitOddEvenList(head);
head2 = reverseList(head2);
head1 = mergeSortedList(head1, head2);
return head1;
}
};