删除链表中重复的节点

class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead)
    {
        ListNode *preNode, *nowNode, *nextNode;
        preNode = pHead;
        nowNode = pHead;
        nextNode = NULL;
        while(nowNode != NULL){
            nextNode = nowNode->next;
            if(nextNode != NULL){
                if(nextNode->val == nowNode->val){
                    while(nextNode != NULL && nextNode->val == nowNode->val){
                        nextNode = nextNode->next;
                    }
                    if(preNode == nowNode){
                        //头结点需要改变
                        pHead = nextNode;
                        preNode = nextNode;
                        nowNode = nextNode;
                    }else{
                        //删掉中间的重复节点
                        preNode->next = nextNode;
                        nowNode = nextNode;
                    }
                }else{
                    //移动preNode节点到当前节点，nowNode节点指向下一个和当前节点值不同的节点
                    if(nowNode != preNode){
                        preNode = nowNode;
                        nowNode = nextNode;
                    }else{
                        //当前节点指向下一个和当前节点值不同的节点
                        nowNode = nextNode;
                    }
                }
            }else{
                break;
            }
        }
        return pHead;
    }
};