leetcode19删除链表倒数第N个节点（记录）C++-优快云博客

本文链接：https://blog.youkuaiyun.com/m0_73496101/article/details/131288799

该文展示了如何使用C++编程语言来实现删除链表中倒数第n个节点的功能。两种方法被提出：一般方法是通过计算链表长度和遍历来找到目标节点，而双指针方法则更高效，通过两个指针，一个快指针先移动n步，然后两个指针同步移动直到快指针到达链表尾部，此时慢指针指向的就是要删除的节点。

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一般方法：

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

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) {}
};

void printflistnode(ListNode *head);

template<class T>
ListNode* constructListnode(vector<T> vec);

class Solution
{
public:
    ListNode *removeNthFromEnd(ListNode *head, int n)
    {
        if (n <= 0)
            return head;
        // 计算链表长度
        int len = 0;
        ListNode *anode = new ListNode();
        anode = head;
        while (anode != nullptr)
        {
            len++;
            anode = anode->next;
        }

        // 查找并删除指定元素
        if (n > len)
            return head;
        else if (n == len)
        {
            head = head->next;
            printflistnode(head);
            return head;
        }
        else
        {
            int reverse_idx = len;
            anode = head;
            while (reverse_idx != n + 1)
            {
                anode = anode->next;
                reverse_idx--;
            }
            anode->next = anode->next->next;
        }
        printflistnode(head);
        return head;
    }
};

int main()
{
    // 构建链表
    vector<int> vec = {1,2,3,4,5};
    ListNode *head=constructListnode(vec);

    // printf链表
    printflistnode(head);

    cout << endl;

    Solution a;
    a.removeNthFromEnd(head, 1);

    // printflistnode(head);

    delete[] head;

    return 0;
}

void printflistnode(ListNode *head)
{
    ListNode *next_node = head;
    while (next_node != nullptr)
    {
        cout << next_node->val;
        next_node = next_node->next;
    }
}

template<class T>
ListNode* constructListnode(vector<T> vec)
{
    ListNode* head=nullptr;
    if (vec.size() > 0)
    {
        head = new ListNode(vec[0]);
        ListNode *last_node = new ListNode();

        for (int i = 1; i < vec.size(); i++)
        {
            if (i == 1)
            {
                head->next = new ListNode(vec[i]);
                last_node = head->next;
            }
            else
            {
                last_node->next = new ListNode(vec[i]);
                last_node = last_node->next;
            }
        }
    }
    return head;
}

双指针方法：

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

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 printflistnode(ListNode *head);

template<class T>
ListNode* constructListnode(vector<T> vec);

class Solution
{
public:
    ListNode *removeNthFromEnd(ListNode *head, int n)
    {
        if(head==nullptr) return head;
        ListNode *fast_ptr=new ListNode();
        fast_ptr=head;
        ListNode *slow_ptr=new ListNode();
        slow_ptr=head;
        int idx=n;
        while(idx--)
        {
            fast_ptr=fast_ptr->next;
            if(fast_ptr==nullptr && idx!=0)
                return head;
        }
        ListNode *last_prt=new ListNode();
        last_prt=head;
        while(fast_ptr!=nullptr)
        {
            fast_ptr=fast_ptr->next;
            last_prt=slow_ptr;
            slow_ptr=slow_ptr->next;
        }
        if(slow_ptr==head)
            head=head->next;
        else
            last_prt->next=slow_ptr->next;
        printflistnode(head);
        return head;
    }
};

int main()
{
    // 构建链表
    vector<int> vec = {1,2,3,4,5,6};
    ListNode *head=constructListnode(vec);

    // printf链表
    printflistnode(head);

    cout << endl;

    Solution a;
    a.removeNthFromEnd(head, 1);

    // printflistnode(head);

    delete[] head;

    return 0;
}

int printflistnode(ListNode *head)
{
    ListNode *next_node = head;
    while (next_node != nullptr)
    {
        cout << next_node->val;
        next_node = next_node->next;
    }
    return 0;
}

template<class T>
ListNode* constructListnode(vector<T> vec)
{
    ListNode* head=nullptr;
    if (vec.size() > 0)
    {
        head = new ListNode(vec[0]);
        ListNode *last_node = new ListNode();

        for (int i = 1; i < vec.size(); i++)
        {
            if (i == 1)
            {
                head->next = new ListNode(vec[i]);
                last_node = head->next;
            }
            else
            {
                last_node->next = new ListNode(vec[i]);
                last_node = last_node->next;
            }
        }
    }
    return head;
}