ARST- 日常打卡 3

/** * 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 r1, r2, *p1=&r1, *p2=&r2, *p=head, *q;        while(p){            q = p->next;            if(p->val < x){                p->next =p1->next; // 永远指向空地址；                p1->next = p;                p1 = p;            } else {                p->next =p2->next;                p2->next = p;                p2 = p;            }            p=q;        }        p1->next = r2.next;        return r1.next;    }};