代码随想录训练营 Day 03：LeetCode 203 707

代码随想录训练营 Day 03：LeetCode 203 707

203. 移除链表元素

题目

解题

分为两步：
更新头结点；
更新非头结点

code

/**
 * 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) {

        while(head != NULL && head->val == val){
            ListNode* tmp = head;
            head = head->next;
            delete tmp;
        }

        ListNode* node = head;
        while(node != NULL && node->next != NULL)
        {
            if(node->next->val == val)
            {
                ListNode* tmp = node->next;
                node->next = node->next->next;
                delete tmp;                
            }
            else{
                node = node->next;
            }                            
        }

        return head;
    }
};
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总结

707. 设计链表

题目

解题

此题目在于考察链表的基本操作，需要熟练掌握

code

class MyLinkedList {
public:

    struct LinkNode{
        int val;
        LinkNode* next;
        LinkNode(int val): val(val), next(NULL){}
    };

    MyLinkedList() {
        _dummyHead = new LinkNode(0);   //虚拟头结点
        _size = 0;
    }
    
    int get(int index) {
        int result = -1;
        if(index < _size && index >= 0)
        {
            LinkNode* cur = _dummyHead->next;
            //for(int i = 0; i <= index; i++)
            while(index--)
            {
                cur = cur->next;
            }
            result = cur->val;
        }
        return result;
    }
    
    void addAtHead(int val) {
        LinkNode* oldhead =_dummyHead->next;
        LinkNode* newhead = new LinkNode(val);
        _dummyHead->next = newhead;
        newhead->next = oldhead;
        _size++;
    }
    
    void addAtTail(int val) {
        LinkNode* endnode =_dummyHead;
        while(endnode->next != NULL)
        {
            endnode = endnode->next;
        }
        LinkNode* newnode = new LinkNode(val);
        endnode->next = newnode;
        newnode->next = NULL;
        _size++;
    }
    
    void addAtIndex(int index, int val) {
        index = index < 0 ? 0 : index;
        if(index == _size )
        {
            //addAtTail(val);
            LinkNode* endnode =_dummyHead;
            while(endnode->next != NULL)
            {
                endnode = endnode->next;
            }
            LinkNode* newnode = new LinkNode(val);
            endnode->next = newnode;
            newnode->next = NULL;
            _size++;
        }
        else if(index < _size )
        {
            LinkNode* curnode =_dummyHead;
            int i = 0;
            while(i < index)
            {
                curnode = curnode->next;
                i++;
            }
            LinkNode* curnode2 = curnode->next;
            LinkNode* newnode = new LinkNode(val);
            curnode->next = newnode;
            newnode->next = curnode2;
            _size++;
        }

    }
    
    void deleteAtIndex(int index) {
        if(index > -1 && index < _size)
        {
            LinkNode* curnode =_dummyHead;
            int i = 0;
            while(i < index )
            {
                curnode = curnode->next;
                i++;
            }
            LinkNode* tmp = curnode->next;
            if(index == _size - 1)
            {
                curnode->next = NULL;
            }
            else
            {
                curnode->next = tmp->next;
            }
            
            //curnode->next = tmp->next;
            delete tmp;
            tmp = NULL;
            _size--;
        }
    }

private:
// 单链表的私有成员变量：（虚拟头结点）、链表长度
// 其余的结点可通过头结点追寻
    LinkNode* _dummyHead;   //
    int _size;
};

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * MyLinkedList* obj = new MyLinkedList();
 * int param_1 = obj->get(index);
 * obj->addAtHead(val);
 * obj->addAtTail(val);
 * obj->addAtIndex(index,val);
 * obj->deleteAtIndex(index);
 */
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总结

对链表的基本构造不太熟悉，注意多多复习