题解 | #链表分割#

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/
class Partition 
{
public:
ListNode* partition(ListNode* pHead, int x)
{
    if (!pHead) return NULL;
    ListNode* pNewHead1 = NULL;//指向小链表
    ListNode* cur1 = NULL;//遍历小链表

    ListNode* pNewHead2 = NULL;//指向大链表
    ListNode* cur2 = NULL;//遍历大链表

    ListNode* cur = pHead;//指向旧链表
    while (cur)//遍历旧链表
    {
        if (cur->val < x)//符合要求，尾插到NewHead1
        {
            if (pNewHead1 == NULL)//新链表1为空
            {
                cur1 = pNewHead1 = cur;
            }
            else//新链表不为空
            {
                cur1->next = cur;
                cur1 = cur1->next;
            }
        }
        else//不符合要求，cur->next >= x，尾插到NewHead2
        {
            if (pNewHead2 == NULL)//新链表2为空
            {
                cur2 = pNewHead2 = cur;
            }
            else//新链表不为空
            {
                cur2->next = cur;
                cur2 = cur2->next;
            }
        }
        cur = cur->next;
    }
    if (cur1 == NULL)
        return pNewHead2;
    if (cur2 == NULL)
        return pNewHead1;
    cur1->next = pNewHead2;
    cur2->next = NULL;
    return pNewHead1;
}
};

用的是无头单链表