双向循环链表详解及C语言简单实现-创新互联

链表是一种物理存储结构上非连续、非顺序的存储结构，数据元素的逻辑顺序是通过链表中的指针链接次序实现的。而双向链表顾名思义通过指针域向前查找或者向后查找，且头结点与尾节点直接相连构成环。

#ifndef DLIST_H
#define DLIST_H

// 数据类型，可根据需要自行定义
#define Item int 

// 链表节点信息 
typedef struct DLNode
{Item item;
    struct DLNode *prev;
    struct DLNode *next;
} DLNode;

typedef struct DList
{int size;
    DLNode *head;
} DList;

// Interfaces 
void InitDList(DList *dlist);
void InsertDlist(DList *dlist);
DLNode *searchDlist(Dlist *dlist);
void DeleteDlist(DList *dlist, const Item data);
void ShowDlist(const DList *dlist);
void freeDList(DList *dlist); 

#endif //DLIST_H

#include#include#include#include

// 初始化双向链表，带头结点
void InitDList(DList *dlist)
{dlist->head = (DLNode *)malloc(sizeof(DLNode));
    if (dlist->head == NULL)
        return;

    dlist->size = 0;
    dlist->head->item = -1;
    dlist->head->prev = dlist->head;
    dlist->head->next = dlist->head;
}

// 链表项数
int DListcounts(DList *dlist)
{assert(dlist);
    return dlist->size;
}

// 插入数据 1）将数据封装成节点    2）插入链表尾
void InsertDList(DList *dlist, const Item data)
{assert(dlist != NULL);
    DLNode *newnode = (DLNode *)malloc(sizeof(DLNode));
    if(newnode == NULL)
    {printf("out of memory !!\n");
        exit(1);
    }

    newnode->item = data;

    newnode->prev = dlist->head->prev;
    newnode->next = dlist->head;
    dlist->head->prev->next = newnode;
    dlist->head->prev = newnode;
    dlist->size++;
}

// 在循环链表中查找指定数据的节点
DLNode *searchDList(DList *dlist, const Item data)
{int i;
    assert(dlist != NULL);
    if(dlist->size == 0)
    {printf("the dlist is empty, do not find element:%d\n", data);
        return NULL;
    }

    DLNode *cur = dlist->head->next;
    for (i = 0; i< dlist->size; i++)
    {if(cur->item == data)
        {printf("find it ^_^!!!\n");
            return cur;
        }
        cur = cur->next;
    }

    if( i == dlist->size)
    {printf("unlucky, the element:%d is not exist in dlsit\n");
        return NULL;
    }
}

// 在双向循环链表中获取指定数据的节点，并返回
void deleteDList(DList *dlist, const Item data)
{DLNode *node = searchDList(dlist, data);
    if(node == NULL)
    {printf("the delete element is not exist in dlist!!\n");
        return;
    }

    node->prev->next = node->next; 
    node->next->prev = node->prev;
    dlist->size--;
    free(node);
    printf("delete it successfully!!\n");
    return ;
}


// 释放构建链表所申请的堆内存
void freeDList(DList *dlist)
{DLNode *cur =NULL, *next = NULL;
    for (cur = dlist->head->next; cur != dlist->head; cur = next)
    {next = cur->next;       // 获取下一个节点
        free(cur);          // 释放节点
    }

    free(dlist->head);
    dlist->head = NULL;
}

// 主函数，对上述各接口调用
int main()
{DList list;
    DLNode *node;
    InitDList(&list);
    InsertDList(&list, 1);
    InsertDList(&list, 2);
    showDList(&list);
    node = searchDList(&list, 3);

    int counts1 = DListcounts(&list);
    printf("the counts of dlist is %d\n", counts1);

    deleteDList(&list, 1);

    int counts2 = DListcounts(&list);
    printf("the counts of dlist is %d\n", counts2);
    showDList(&list);
    freeDList(&list);
    return 0;
}

[postgres@test dlist_test]$ ./Dlist
1       2
unlucky, the element:3 is not exist in dlsit
the counts of dlist is 2
find it ^_^!!!
delete it successfully!!
the counts of dlist is 1
2

class Solution {public:
    Node* copyRandomList(Node* head) {if(head == nullptr) return nullptr;
        Node* cur = head;
        // 1. 复制各节点，并构建拼接链表
        while(cur != nullptr) {Node* tmp = new Node(cur->val);
            tmp->next = cur->next;
            cur->next = tmp;
            cur = tmp->next;
        }
        // 2. 构建各新节点的 random 指向
        cur = head;
        while(cur != nullptr) {if(cur->random != nullptr)
                cur->next->random = cur->random->next;
            cur = cur->next->next;
        }
        // 3. 拆分两链表
        cur = head->next;
        Node* pre = head, *res = head->next;
        while(cur->next != nullptr) {pre->next = pre->next->next;
            cur->next = cur->next->next;
            pre = pre->next;
            cur = cur->next;
        }
        pre->next = nullptr; // 单独处理原链表尾节点
        return res;      // 返回新链表头节点
    }
};

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