题解 | #划分链表#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @param x int整型 
     * @return ListNode类
     */
    ListNode* partition(ListNode* head, int x) {
        // write code here
        if(!head || !head->next)
            return head;
        ListNode* start = new ListNode(-1);
        start->next = head;
        auto p = head;
        while(p->next != nullptr) p = p->next;
        auto q = start;
        auto end = p;
        while(q->next != end) {
            if(q->next->val >= x) {
                p->next = q->next;
                q->next = q->next->next;
                p->next->next = nullptr;
                p = p->next;
            }else {
                q = q->next;
            }
        }
        if(end->val >= x) { // 特判
            p->next = end;
            q->next = end->next;
            end->next = nullptr;
        }
        return start->next;
    }
};