刷题笔记-链表

完整链表操作模板

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#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

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) {}
    };
    MyLinkedList() {
        _size = 0;
        _dummyHead = new ListNode(0);
    }
    int get(int index) {
        if (index > _size - 1 || index < 0) {
            return -1;
        }
        ListNode* cur = _dummyHead;
        while (index--) {
            cur = cur->next;
        }
        return cur->next->val;
    }
    void addAtHead(int val) {
        ListNode* newNode = new ListNode(val);
        newNode->next = _dummyHead->next;
        _dummyHead->next = newNode;
        _size++;
    }
    void addAtTail(int val) {
        ListNode* newNode = new ListNode(val);
        ListNode* cur = _dummyHead;
        while (cur->next != nullptr) {
            cur = cur->next;
        }
        cur->next = newNode;

        _size++;
    }

    void addAtIndex(int index, int val) {
        if (index > _size) {
            return;
        }
        if (index <= 0) {
            addAtHead(val);
            return;
        }
        if (index == _size) {
            addAtTail(val);
            return;
        }
        ListNode* newNode = new ListNode(val);
        ListNode* cur = _dummyHead;
        while (index--) {
            cur = cur->next;
        }
        newNode->next = cur->next;
        cur->next = newNode;
        _size++;
    }
    void deleteAtIndex(int index) {
        if (index < 0 || index > _size - 1) {
            cout << "index out of range!" << endl;
            return;
        }
        ListNode* cur = _dummyHead;
        while (index--) {
            cur = cur->next;
        }
        ListNode* temp = cur->next;
        cur->next = cur->next->next;
        delete temp;
        _size--;
    }
    void printLinkedList() {
        ListNode* cur = _dummyHead;
        while (cur->next != nullptr) {
            cout << cur->next->val << " ";
            cur = cur->next;
        }
        cout << endl;
    }
    void reverseList() {
        ListNode* temp;
        ListNode* cur = _dummyHead->next;
        ListNode* pre = nullptr;
        while (cur) {
            temp = cur->next;  // 保存一下
                               // cur的下一个节点，因为接下来要改变cur->next
            cur->next = pre;  // 翻转操作
            // 更新pre 和 cur指针
            pre = cur;
            cur = temp;
        }
        _dummyHead->next = pre;
    }

    void removeNthFromEnd(int n) {
        ListNode* slow = _dummyHead;
        ListNode* fast = _dummyHead;
        while (n-- && fast != nullptr) {
            fast = fast->next;
        }
        if (fast == nullptr) {
            return;
        }
        while (fast->next != nullptr) {
            slow = slow->next;
            fast = fast->next;
        }
        ListNode* tem = slow->next;
        slow->next = slow->next->next;
        delete tem;
    }
    
       void swap() {// 两两节点交换
        ListNode* cur = _dummyHead;
        while (cur->next != nullptr && cur->next->next != nullptr) {
            ListNode* tmp = cur->next;               // 记录临时节点
            ListNode* tmp1 = cur->next->next->next;  // 记录临时节点

            cur->next = cur->next->next;   // 步骤一
            cur->next->next = tmp;         // 步骤二
            cur->next->next->next = tmp1;  // 步骤三

            cur = cur->next->next;  // cur移动两位，准备下一轮交换
        }
    }

       private:
        int _size;
        ListNode* _dummyHead;
    };

int main() {
    MyLinkedList linkedList;
    linkedList.addAtHead(1);
    linkedList.addAtHead(2);
    linkedList.addAtHead(3);
    linkedList.addAtTail(3);
    // linkedList.reverseList();
    linkedList.printLinkedList();
    // cout<<linkedList.get(2);
}

https://leetcode-cn.com/problems/linked-list-cycle-ii/

反转链表

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public void reverseList(ListNode head) {
    ListNode tmp = null;
    ListNode pre = null;
    ListNode cur = head;
    while (cur != null) {
        tmp = cur.next;
        cur.next = pre;
        pre = cur;
        cur = tmp;
    }
}