题解 | #链表分割# - C - 哨兵卫 + 尾插新链表

struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/
class Partition {
public:
    ListNode* partition(ListNode* pHead, int x) {
        // write code here
        //大体思路：创建两个链表，一个存储小于x的值，一个存储大于x的值，遍历原链表进行尾插。
        //创建哨兵卫
        struct ListNode* greatHead, *greattail, *lessHead, *lesstail, *cur;
        greatHead = greattail = (struct ListNode*)malloc(sizeof(struct ListNode));
        lessHead = lesstail = (struct ListNode*)malloc(sizeof(struct ListNode));
        cur = pHead;
        
        //遍历原链表进行尾插
        while(cur)
        {
            if(cur->val < x)
            {
                lesstail->next = cur;  //链接原链表头节点
                lesstail = cur;    //更新less链表尾节点
                cur = cur->next;  //原链表中cur继续更新往下走
            }
            else
            {
                greattail->next = cur;
                greattail = cur;
                cur = cur->next;
            }
        }
        
        lesstail->next = greatHead->next;  //链接less链表和geart链表
        greattail->next = NULL;   //注意处理最后一个节点的原链接关系
        
        return lessHead->next;
    }
};