LintCode 96. 链表划分

思路：

遍历链表,用两个链表进行记录,遍历完成之后直接操作两个链表.

代码：

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param head: The first node of linked list.
     * @param x: an integer
     * @return: a ListNode 
     */
    ListNode *partition(ListNode *head, int x) {
        // write your code here
        ListNode *small_head = nullptr, *small_tail = nullptr;
        ListNode *big_head = nullptr, *big_tail = nullptr;
        ListNode *tmp;
        while(head){
            tmp = head;
            head = head->next;
            tmp->next = nullptr;
            if(tmp->val < x)
                insertNode(small_head, small_tail, tmp);
            else
                insertNode(big_head, big_tail, tmp);
        }// while
        if(!small_head)
            return big_head;
        else if(!big_head)
            return small_head;
        small_tail->next = big_head;
        return small_head;
    }
    void insertNode(ListNode *&head, ListNode *&tail, ListNode *node){
        if(!head){
            head = node;
            tail = node;
            return;
        }
        tail->next = node;
        tail = tail->next;
    }// insertNode
};