链表分割

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/
class Partition {
public:
    ListNode* partition(ListNode* pHead, int x) {
        // write code here
        if(!pHead || !pHead->next)
            return pHead;
        
       
        ListNode* littleBegin = new ListNode(-1);
        ListNode* bigBegin = new ListNode(-1);
        ListNode* little = littleBegin;
        ListNode* big = bigBegin;
        
        ListNode* pWork = pHead;
        while(pWork){
            if(pWork->val < x){
                little->next = pWork;
                little = little->next;
            }else{
                big->next = pWork;
                big = big->next;
            }
            pWork = pWork->next;
        }
        
           little->next = bigBegin->next;
        big->next = nullptr;
        return littleBegin->next;
        
    }
};
//思路为建立两个链表little中存放比x小的元素，big中存放比x大的元素。
//之后合并little和big两个链表。