静态双向链表的单数组实现

结构体及相关函数声明如下：

typedef struct ITEM {
    int key;
    void * statellite;
} item_t;
typedef struct STATIC_SINGLE_ARRAY_DOUBLE_LINKED_LIST
{
    int size;
    int count;
    int head;
    int free;
    item_t * array;
} SSADLL;
void SSADLL_traverse(SSADLL * L);
SSADLL* SSADLL_init(int size);
item_t* SSADLL_get_object(SSADLL * L, int location);
item_t* SSADLL_get_next(SSADLL * L, int location);
item_t* SSADLL_get_prev(SSADLL * L, int location);
int SSADLL_free(SSADLL * L, int location);
int SSADLL_allocate(SSADLL * L);
int SSADLL_insert(SSADLL * L, item_t item);
int SSADLL_search(SSADLL * L, item_t item);
int SSADLL_delete(SSADLL * L, item_t item);

各函数实现如下：

//functions for static single array double linked list
void SSADLL_traverse(SSADLL * L) {
    if (L == NULL) {
        fprintf(stderr, "Not initialized.\n");
        return;
    }
    if (L->head == 0) {
        fprintf(stderr, "Empty linked list.\n");
    }
    int location = L->head;
    printf("Total elements number is %3d. Linked list size is %3d.\n", L->count, L->size);
    while (location != 0) {
        printf("%3d item prev is %3d, location is %3d, next is %3d.\n", \
            SSADLL_get_object(L, location)->key, SSADLL_get_prev(L, location)->key, location, \
            SSADLL_get_next(L, location)->key);
        location = SSADLL_get_next(L, location)->key;
    }
    int free = L->free;
    while (free != 0) {
        printf("Free space is %3d, next is: %3d\n", free, SSADLL_get_next(L, free)->key);
        free = SSADLL_get_next(L, free)->key;
    }
}
item_t* SSADLL_get_object(SSADLL * L, int location) {
    return L->array + 3 * (location - 1);
}
item_t* SSADLL_get_next(SSADLL * L, int location) {
    return L->array + 3 * (location - 1) + 1;
}
item_t* SSADLL_get_prev(SSADLL * L, int location) {
    return L->array + 3 * (location - 1) + 2;
}
SSADLL* SSADLL_init(int size) {
    SSADLL * L = (SSADLL*)malloc(sizeof(SSADLL));
    if (!L) {
        fprintf(stderr, "Static single array double linked list init fail.\n");
        return NULL;
    }
    L->size = size;
    L->count = 0;
    L->head = 0;
    L->free = size;
    L->array = (item_t*)calloc(size * 3, sizeof(item_t));
    if (!L->array) {
        fprintf(stderr, "Static single array double linked list init fail.\n");
        return NULL;
    }
    for (int i = size; i > 0; i--) {
        SSADLL_get_next(L, i)->key = i - 1;
    }
    return L;
}
int SSADLL_free(SSADLL * L, int location) {
    if (location <= 0 || location > L->size) {
        fprintf(stderr, "Out of range.\n");
        return 0;
    }
    SSADLL_get_next(L, location)->key = L->free;
    L->free = location;
    return 1;
}
int SSADLL_allocate(SSADLL * L) {
    if (L->free == 0) {
        fprintf(stderr, "Out of range.\n");
        return 0;
    }
    int x = L->free;
    L->free = SSADLL_get_next(L, L->free)->key;
    return x;
}
int SSADLL_insert(SSADLL * L, item_t item) {
    if (L == NULL) {
        fprintf(stderr, "Not initialized.\n");
        return 0;
    }
    int obj = SSADLL_allocate(L);
    if (obj == 0) {
        fprintf(stderr, "Out of range.\n");
        return obj;
    }
    *SSADLL_get_object(L, obj) = item;
    SSADLL_get_next(L, obj)->key = L->head;
    SSADLL_get_prev(L, obj)->key = 0;
    L->count++;
    if (L->head != 0)
        SSADLL_get_prev(L, L->head)->key = obj;
    L->head = obj;
    return obj;
}
int SSADLL_search(SSADLL * L, item_t item) {
    if (L == NULL) {
        fprintf(stderr, "Not initialized.\n");
        return 0;
    }
    if (L->head == 0) {
        fprintf(stderr, "Empty linked list.\n");
        return 0;
    }
    int location = L->head;
    while (location != 0) {
        if (SSADLL_get_object(L, location)->key == item.key) {
            return location;
        }
        location = SSADLL_get_next(L, location)->key;
    }
    fprintf(stderr, "Item cannot be found.\n");
    return 0;
}
int SSADLL_delete(SSADLL * L, item_t item) {
    int location = SSADLL_search(L, item);
    if (location == 0) {
        fprintf(stderr, "Delete fail.\n");
        return 0;
    }
    if (SSADLL_get_next(L, location)->key) {
        SSADLL_get_prev(L, SSADLL_get_next(L, location)->key)->key = SSADLL_get_prev(L, location)->key;
    }
    if (SSADLL_get_prev(L, location)->key) {
        SSADLL_get_next(L, SSADLL_get_prev(L, location)->key)->key = SSADLL_get_next(L, location)->key;
    }
    if (location == L->head) {
        L->head = SSADLL_get_next(L, location)->key;
    }
    L->count--;
    return SSADLL_free(L, location);
}
//--------------------------------------------------------------------------

关键在于next和prev的获取，可用如下代码进行测试：

void test_for_SSADLL() {
    SSADLL * L = SSADLL_init(SIZE);
    for (int i = 0; i < 10; i++) {
        item_t item = {i + 10, NULL};
        SSADLL_insert(L,item);
    }
    SSADLL_traverse(L);
    for (int i = 0; i < 10; i++) {
        item_t item = {i + 10, NULL};
        SSADLL_delete(L, item);
    }
    SSADLL_traverse(L);
    printf("-------------------------------------------------------------------\n");
    for (int i = 0; i <= 10; i++) {
        item_t item = {i + 10, NULL};
        SSADLL_insert(L, item);
    }
    for (int i = 4; i >= -2; i--) {
        item_t item = {i + 10, NULL};
        SSADLL_delete(L, item);
    }
    for (int i = 0; i <= 10; i++) {
        item_t item = {i - 10, NULL};
        SSADLL_insert(L, item);
    }
    for (int i = -10; i <= 17; i++) {
        item_t item = {i, NULL};
        SSADLL_delete(L, item);
    }
    SSADLL_traverse(L);
}

关于静态双向链表的单数组表示的相关内容可见算法导论第三版10.3小结，以及10.3-2题。