56 lines
1.4 KiB
C++
56 lines
1.4 KiB
C++
/**
|
|
* 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 {
|
|
ListNode* update_tail(ListNode* tail, ListNode* node) const
|
|
{
|
|
if (tail != nullptr) {
|
|
tail->next = node;
|
|
}
|
|
return node;
|
|
}
|
|
|
|
public:
|
|
ListNode* partition(ListNode* head, int x)
|
|
{
|
|
ListNode* left_head = nullptr;
|
|
ListNode* right_head = nullptr;
|
|
|
|
ListNode* left_tail = nullptr;
|
|
ListNode* right_tail = nullptr;
|
|
|
|
while (head != nullptr) {
|
|
auto next_head = head->next;
|
|
|
|
if (head->val < x) {
|
|
left_tail = update_tail(left_tail, head);
|
|
} else {
|
|
right_tail = update_tail(right_tail, head);
|
|
}
|
|
|
|
if (left_head == nullptr) {
|
|
left_head = left_tail;
|
|
}
|
|
if (right_head == nullptr) {
|
|
right_head = right_tail;
|
|
}
|
|
|
|
head = next_head;
|
|
}
|
|
|
|
left_tail = update_tail(left_tail, right_head);
|
|
right_tail = update_tail(right_tail, nullptr);
|
|
|
|
if (left_head == nullptr) {
|
|
return left_tail;
|
|
}
|
|
return left_head;
|
|
}
|
|
};
|