Question

我正在尝试交换双向链表的第一个和最后一个元素。到目前为止，我有以下代码，我在其中创建一个列表并添加一些数字。但输出两次都是相同的列表。

#include <stdio.h>
#include <stdlib.h>

struct node2 {
    int number;
    struct node2 *next, *prev;
};

void addNodeDouble(struct node2 **head, struct node2 **tail, int num, int thesi) {
    if (*head == NULL) {
        struct node2 * current;
        current = (struct node2 *)malloc(1 * sizeof(struct node2));
        current->number = num;
        current->prev = NULL;
        current->next = NULL;
        *head = current;
        *tail = current;
    } else {
        if (thesi == 1) {
            struct node2 *current, *temp;
            current = (struct node2 *)malloc(1 * sizeof(struct node2));
            current->number = num;
            temp = *head;
            while (temp->next != NULL)
                temp = temp->next;

            temp->next = current;
            current->prev = *tail;
            current->next = NULL;
            (*tail)->next = current;
            *tail = current;
        } else  {
            struct node2 *current;
            current = (struct node2 *)malloc(1 * sizeof(struct node2));
            current->number = num;
            current->next = *head;
            (*head)->prev = current;
            *head = current;
        }
    }
}

void ReversedisplayList(struct node2 **head, struct node2 **tail) {
    struct node2 *current;
    if (*head == NULL)
        printf("I lista einai adeia!\n");
    else {
        current = *tail;
        while (current != NULL) {
            printf("%d ", current->number);
            current = current->prev;
        }
    }
}

void swapElements2(struct node2 **head, struct node2 **tail) {
    struct node2 *current, *temp;

    temp = (*tail)->prev;
    current = *tail;

    temp->next = *head;
    current->next = (*head)->next;
    (*head)->next = NULL;
    *head = current;
}

int main() {
    struct node2 *head, *tail;
    head = tail = NULL;

    addNodeDouble(&head, &tail, 4, 1);
    addNodeDouble(&head, &tail, 8, 1);
    addNodeDouble(&head, &tail, 3, 0);
    addNodeDouble(&head, &tail, 1, 1);
    addNodeDouble(&head, &tail, 7, 0);

    printf("\n\nDoubly linked list (reversed): ");
    ReversedisplayList(&head, &tail);

    swapElements2(&head, &tail);
    printf("\nChanged list: ");
    ReversedisplayList(&head, &tail);
}

我明白了：

Doubly linked list (reversed): 1 8 4 3 7 
Changed list: 1 8 4 3 7

但我想：

Changed list: 7 8 4 3 1

Answer 1

要交换第一个以及头部和尾部元素，您必须完成以下过程。首先，我们必须在一些临时变量中得到尾部的前一个节点和头部的下一个节点，并交换头部和尾部的下一个和上一个指针。

void swapElements2(struct node2 **head, struct node2 **tail) {
    struct node2 *ttail, *thead;

    ttail = (*tail) -> prev;
    thead = (*head) -> next;

    (*head) -> next = NULL;
    (*tail) -> prev = NULL;

    (*head) -> prev = ttail;
    (*tail) -> next = thead;

    ttail -> next = (*head);
    thead -> prev = (*tail);

    (*tail)  = ttail -> next;
    (*head)  = thead -> next;
}

Answer 2

您忘记更改(*head) -> prev和(*tail) -> prev。

(*head)->prev = temp;
(*tail)->prev = NULL;

C - 交换双向链表中的第一个和最后一个元素

2 个答案: