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

// 定義節點結構
typedef struct Node {
    int data;
    struct Node* prev;
    struct Node* next;
} Node;

// 定義雙向鏈結串列結構
typedef struct {
    Node* head;
    Node* tail;
} DoublyLinkedList;

// 初始化雙向鏈結串列
void initList(DoublyLinkedList* list) {
    list->head = NULL;
    list->tail = NULL;
}

// 在尾部插入新節點
void insertAtTail(DoublyLinkedList* list, int data) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    newNode->data = data;
    newNode->next = NULL;

    if (list->tail == NULL) {
        newNode->prev = NULL;
        list->head = newNode;
        list->tail = newNode;
    } else {
        newNode->prev = list->tail;
        list->tail->next = newNode;
        list->tail = newNode;
    }
}

// 從頭到尾遍歷並印出串列
void printListForward(DoublyLinkedList* list) {
    Node* current = list->head;
    printf("從頭到尾: ");
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}

// 從尾到頭遍歷並印出串列
void printListBackward(DoublyLinkedList* list) {
    Node* current = list->tail;
    printf("從尾到頭: ");
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->prev;
    }
    printf("\n");
}

// 主函數示例
int main() {
    DoublyLinkedList list;
    initList(&list);

    insertAtTail(&list, 10);
    insertAtTail(&list, 20);
    insertAtTail(&list, 30);

    printListForward(&list);
    printListBackward(&list);

    return 0;
}