1.移除链表元素

LeetCode 203

题目：LeetCode203 | 移除链表元素

直接使用原来的链表来进行删除操作

class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        while(head != NULL && head ->val == val){
            ListNode *temp = head;
            head = head -> next;
            delete temp;
        }
        ListNode *cur = head;
        while(cur != NULL && cur -> next != NULL){
            if(cur -> next -> val == val){
                ListNode *temp = cur -> next;
                cur ->next = cur -> next -> next;
                delete temp;
            }
            else{
                cur = cur -> next;
            }
        }
        return head;
    }
};

设置一个虚拟头结点再进行删除操作

class Solution{
public:
    ListNode* removeElements(ListNode* head, int val){
        ListNode *dummyHead = (ListNode *)malloc(sizeof(ListNode));
        dummyHead -> next = head;
        ListNode *cur = dummyHead;
        while(cur -> next != NULL){
            if(cur -> next -> val == val){
                ListNode *temp = cur -> next;
                cur ->next = cur -> next -> next;
                delete temp;
            }
            else{
                cur = cur -> next;
            }
        }
        head = dummyHead -> next;
        free(dummyHead);
        return head;
    }
};

2.设计链表

LeetCode 707

题目：LeetCode 707 | 设计链表

class MyLinkedList {
public:
    struct LinkedNode{
        int val;
        LinkedNode* next;
        LinkedNode(int val) : val(val), next(NULL){}
    };

    MyLinkedList() {
        dummyHead = new LinkedNode(0);
        size = 0;
    }
    
    int get(int index) {
        if(index > (size - 1) || index < 0){
            return -1;
        }
        LinkedNode* cur = dummyHead ->next;
        while(index){
            cur = cur -> next;
            index--;
        }
        return cur -> val;
    }
    
    void addAtHead(int val) {
        LinkedNode* newNode = new LinkedNode(val);
        newNode -> next = dummyHead -> next;
        dummyHead -> next = newNode;
        size++;
    }
    
    void addAtTail(int val) {
        LinkedNode* newNode = new LinkedNode(val);
        LinkedNode* cur = dummyHead;
        while(cur -> next != NULL){
            cur = cur -> next;
        }
        cur -> next = newNode;
        size++; 
    }
    
    void addAtIndex(int index, int val) {
        if(index > size || index < 0)
            return;
        LinkedNode* newNode = new LinkedNode(val);
        LinkedNode* cur = dummyHead;
        while(index){
            cur = cur -> next;
            index--;
        }
        newNode -> next = cur -> next;
        cur -> next = newNode;
        size++;
    }
    
    void deleteAtIndex(int index) {
        if (index >= size || index < 0) {
            return;
        }
        LinkedNode* cur = dummyHead;
        while(index) {
            cur = cur ->next;
            index--;
        }
        LinkedNode* temp = cur->next;
        cur->next = cur->next->next;
        delete temp;
        size--;
    }
    void printLinkedList() {
        LinkedNode* cur = dummyHead;
        while (cur->next != NULL) {
            cout << cur->next->val << " ";
            cur = cur->next;
        }
        cout << endl;
    }
private:
    int size;
    LinkedNode* dummyHead;   
};

3.反转链表

LeetCode 206

题目：LeetCode 206 | 反转链表

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* cur = head;
        ListNode* pre = NULL;
        ListNode* temp = NULL;
        while(cur){
            temp = cur->next;
            cur->next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
};