P1【练习力扣203,206】【数据结构】【链表LinkedList】C++版

【203】 移除链表元素

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        ListNode* dummy = new ListNode(0, head);
        ListNode* temp = dummy;
        while(temp->next){
            if(temp->next->val == val){
                temp->next = temp->next->next;
            }else{
                temp = temp->next;
            }
        }

        return dummy->next;
    }
};

time:23:26

【206】反转链表

// 将一个个结点取出，重新组成链表
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* dummy_Node = new ListNode(0, head);
        while(head != NULL && head->next != NULL){
            ListNode* dnext = dummy_Node->next;
            ListNode* hnext = head->next;
            dummy_Node->next = hnext;
            head->next = hnext->next;
            hnext->next = dnext;  
        }
        
        return dummy_Node->next;
        
    }
};

time:30

总结：应理解dummy_Node的含义，指向头结点的哑节点。