从零开始的LeetCode刷题日记：707.设计链表

一.相关链接

题目链接 ：707.设计链表

二.心得体会

这道题也是一道链表题，使用虚拟头节点来处理。整体的逻辑都是很简单的，需要注意的是判断索引值是否合理的时候，需要注意按索引增加链表节点时要比get和delete多一位，即>len。

三.代码

/**
 * 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 MyLinkedList {
public:
    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) {}
    };
    int _len;
    ListNode* _dummy_head;
    MyLinkedList() {
        _dummy_head = new ListNode(0);
        _len = 0;
    }

    int get(int index) {
        if(index<0||index>_len-1) return -1;
        ListNode* p = _dummy_head;
        for(int i=0;i<=index;i++){
            p = p->next;
        }
        int ans = p->val;
        return ans;
    }
    
    void addAtHead(int val) {
        ListNode* p = new ListNode(val);
        p->next = _dummy_head->next;
        _dummy_head->next = p;
        _len++;
        return ;
    }
    
    void addAtTail(int val) {
        ListNode* p = _dummy_head;
        ListNode* tail = new ListNode(val);
        for(int i=0;i<_len;i++){
            p = p->next;
        }
        p->next = tail;
        _len++;
        return ;
    }
    
    void addAtIndex(int index, int val) {
        if(index<0||index>_len) return;
        ListNode* p = _dummy_head;
        ListNode* index_node = new ListNode(val);
        for(int i=0;i<index;i++){
            p = p->next;
        }
        index_node->next = p->next;
        p->next = index_node;
        _len++;
        return ;
    }
    
    void deleteAtIndex(int index) {
        if(index<0||index>_len-1) return;
        ListNode* p = _dummy_head;
        for(int i=0;i<index;i++){
            p = p->next;
        }
        ListNode* tmp = p->next;
        p->next = tmp->next;
        delete tmp;
        _len--;
        return ;
    }
};

/**
 * 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);
 */