NC23：划分链表

解法1：模拟

public ListNode partition (ListNode head, int x) {
        // write code here
        ListNode small=new ListNode(0);
        ListNode smallHead=small;
        ListNode large=new ListNode(0);
        ListNode largeHead=large;

        while(head!=null){
            if(head.val<x){
                small.next=head;
                small=small.next;
            }
            else{
                large.next=head;
                large=large.next;
            }
            head=head.next;
        }
        large.next=null;
        small.next=largeHead.next;
        return smallHead.next;
    }