https://leetcode-cn.com/problems/partition-list/description/
给定一个链表和一个特定值 x，对链表进行分隔，使得所有小于 x 的节点都在大于或等于 x 的节点之前。
你应当保留两个分区中每个节点的初始相对位置。
示例:
输入: head = 1->4->3->2->5->2, x = 3
输出: 1->2->2->4->3->5
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* partition(ListNode* head, int x) {
if(!head || !head->next){
return head;
}
ListNode* Head1 = new ListNode(-1);
ListNode* cur1 = Head1;
ListNode* Head2 = new ListNode(-1);
ListNode* cur2 = Head2;
while(head){
if(head->val < x){
cur1->next = head;
cur1 = cur1->next;
}
else{
cur2->next = head;
cur2 = cur2->next;
}
head = head->next;
}
cur2->next = NULL;
cur1->next = Head2->next;
return Head1->next;
}
};