C - Das erste und letzte Element in der doppelt verketteten Liste vertauschen

Question

Ich versuche, die ersten und letzten Elemente einer doppelt verketteten Liste zu vertauschen. Bisher habe ich den folgenden Code, wo ich eine Liste erstellen und einige Nummern hinzufügen. Aber die Ausgabe ist die gleiche Liste beide Male.

#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); 
} 

ich:

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

Aber ich will:

Changed list: 7 8 4 3 1 

Answer 1

Um die ersten und Kopf- und Schwanzelemente zu tauschen, gehen Sie wie folgt vor. Zuerst müssen wir den vorherigen Knoten des Schwanzes und den nächsten Knoten des Kopfes in eine temporäre Variable bringen und Kopf und Schwanz des nächsten und vorherigen Zeigers austauschen.

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

Sie (*head) -> prev und (*tail) -> prev zu ändern vergessen.

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