Partition List

题目：Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

分析：链表的特点在于不存在固定大小的存储区域，节点可以任意移动，插入。算法：遍历链表，分别插入两个新链表，一个小于x，一个大于等于x。然后把后者拼接在前者之后。

ListNode *partition(ListNode *head, int x) {        if(!head||!head->next) return head;        ListNode dummy_left(-1),dummy_right(-1);        ListNode *cur_left = &dummy_left, *cur_right = &dummy_right;        while(head)        {            if(head->val<x)            {                cur_left->next=head;                cur_left=head;            }            else            {                cur_right->next=head;                cur_right=head;            }            head=head->next;        }        cur_left->next=dummy_right.next;        cur_right->next= NULL;        return dummy_left.next;    }