思路:把小于x的值放到less中,大于等于x的放到more中,保持原序,最后再拷贝回原链表中。
class Solution {
public:
ListNode* partition(ListNode* head, int x) {
if(head==NULL||head->next==NULL)
return head;
vector<ListNode> less, more;
ListNode *p = head;
while (p) {
if (p->val < x)
less.push_back(*p);
else
more.push_back(*p);
p = p->next;
}
//特殊情况:全部比x大或者全部比x小时,无需划分
if(less.empty()||more.empty())
return head;
//填入过程中,建立好next指针,不能直接返回&less[0],因为结束后vector会被析构,这个地址将变成无效
size_t i = 0;
for (;i < less.size()-1;++i) {
less[i].next = &less[i + 1];
}
less[i].next = &more[0];
size_t j = 0;
for (;j < more.size()-1;++j) {
more[j].next = &more[j + 1];
}
more[more.size() - 1].next = NULL;
//拷贝回原链表,直接修改节点的值即可,两个同时往后走,修改值即可
p = head;
ListNode *NewHead = &less[0];
while (p) {
p->val = NewHead->val;
p = p->next;
NewHead = NewHead->next;
}
return head;
}
};