C++ 代码实现【环形链表】判断链表是否有环以及寻找环的起点

最新推荐文章于 2025-03-06 16:36:53 发布

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最新推荐文章于 2025-03-06 16:36:53 发布

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文章标签： c++ 链表开发语言

本文链接：https://blog.youkuaiyun.com/m0_50096385/article/details/131406192

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该代码示例展示了如何在C++中创建一个循环链表，并提供了一个函数用于检测链表是否存在环。程序首先定义了一个结构体Lnode表示链表节点，接着创建并初始化循环链表。然后，通过快慢指针法检查链表中是否有环，若存在环则输出相关信息。

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#include <iostream>

struct Lnode
{
    char data;
    Lnode *next;
};


Lnode* Creat_Circle_Lnode(int n){
    if (n < 3)
    {
        throw "little than 3";
    }
     // head pointer
    Lnode *head = new Lnode;
    // head lnode
    Lnode *head_lnode = new Lnode;
    Lnode *r = new Lnode;
    head_lnode = r;
    for (int i = 0; i < n; i++)
    {
        
        Lnode *p = new Lnode;
        std::cout<<"Input marks to this Lnode:";
        p->data = getchar();
        while (std::cin.get() != '\n');
        r->next = p;
        r = p;
    }
    Lnode *l = new Lnode;
    l = head_lnode;
    for (int i = 0; i < n - 3; i++)
    {
        l = l->next;
    }
   
    r->next = l;
    
    head->next = head_lnode;
    head_lnode =NULL;
    l = nullptr;
    r = nullptr;
    return head;
}

void test(){
    Lnode *p = new Lnode;
    try
    {
        
        p = Creat_Circle_Lnode(5);
    }
    catch(const std::exception& e)
    {
        std::cerr << e.what() << '\n';
    }
    
    // Judege if has circle
    // to creat the fast_pointer and low_pointers
    Lnode *fast_pointer = new Lnode;
    Lnode *low_pointer = new Lnode;
    fast_pointer = low_pointer = p;
    while (fast_pointer->next != NULL && fast_pointer->next->next != nullptr)
    {
        low_pointer = low_pointer->next;
        fast_pointer = fast_pointer->next->next;
        if (fast_pointer == low_pointer)
        {
            std::cout<<"链表有环"<<std::endl;
            break;
        }
       
    }
    low_pointer = p;
    while (low_pointer != fast_pointer)
    {
        low_pointer = low_pointer->next;
        fast_pointer = fast_pointer->next;
    }
    std::cout<<"The mark of enterance: "<<fast_pointer->data<<std::endl;
}


int main(void){
   test();
    return 0;
}