86. Partition List

    /*
     * 86. Partition List 
     * 11.26 by Mingyang
     * 没有什么诀窍，就是分成两个list，一个装小的一个装大的
     * 只是注意small.next = head;赋值要准确，不能够错误，不能small=head
     */
    public ListNode partition(ListNode head, int x) {
        if (head == null || head.next == null)
            return head;
        ListNode small = new ListNode(-1);
        ListNode newsmallhead = small;
        ListNode big = new ListNode(-1);
        ListNode newbighead = big;
        while (head != null) {
            if (head.val < x) {
                small.next = head;
                small = small.next;
            } else {
                big.next = head;
                big = big.next;
            }
            head = head.next;
        }
        big.next = null;
        small.next = newbighead.next;
        return newsmallhead.next;
    }