题解 | #删除有序链表中重复的元素-I#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* deleteDuplicates(ListNode* head) {
        // write code here
        ListNode* fast = head->next;
        ListNode* slow = head;
        ListNode* fast_next = nullptr;
        fast_next = fast->next;
        if(slow == nullptr) //空表
        {
            return nullptr;
        }
        if(fast == nullptr) //单元素表
        {
            return head;
        }
        if((slow->val == fast->val)&&(fast_next == nullptr))//两元素表相同
        {
            return fast;
        }
        if((slow->val != fast->val)&&(fast_next == nullptr))//两元素表不同
        {
            return head;
        }
        fast = head->next;
        slow = head;
       while(fast != nullptr)
        {
            if(fast->val == slow->val)
            {
                slow->next = fast ->next; 
                fast = fast ->next;
               
            }
            else
            {
                fast = fast ->next;
                slow = slow ->next;
            }
        }
        return head;
    }
};