Solution.cpp

/**
 * 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* partition(ListNode* head, int x) {
        ListNode* l1 = new ListNode();
        ListNode* l2 = new ListNode();
        ListNode* cur1 = l1;
        ListNode* cur2 = l2;
        while (head != nullptr) {
            if (head->val < x) {
                cur1->next = head;
                cur1 = cur1->next;
            } else {
                cur2->next = head;
                cur2 = cur2->next;
            }
            head = head->next;
        }
        cur1->next = l2->next;
        cur2->next = nullptr;
        return l1->next;
    }
};