本代碼是參考《算法導論》講解實作的,自用,閱讀時對照書本便于了解相關變量定義。
// 算法導論版本B樹
typedef int KEY_TYPE;
typedef struct _btree_node
{
//struct btree_node *children[M * 2];
struct _btree_node **childrens; //大小靈活
//KEY_TYPE keys[2 * M - 1];
KEY_TYPE *keys;
int num; //key的數量
int leaf; //是否為葉子
} btree_node;
typedef struct _btree
{
struct btree_node *root;
int t; // 除根節點外,每個節點的最小孩子數量
// key的最大數量為2t - 1, 一個内節點孩子節點數量最多為2t
} btree;
// desc:建立一個節點
// t:代表節點子樹最大數量的一半(M/2)
// leaf: 是否為葉節點
struct btree_node *btree_create_node(int t, int leaf)
{
struct btree_node *node = (btree_node *)calloc(1, sizeof(btree_node));
//assert的作用是現計算表達式 expression ,
//如果其值為假(即為0),那麼它先向stderr列印一條出錯資訊,
//然後通過調用 abort 來終止程式運作。
if(node == NULL) assert(0);
node->leaf = leaf;
node->keys = (KEY_TYPE *)calloc(1, (2 * t - 1)*sizeof(KEY_TYPE));
node->childrens = (btree_node **)calloc(1, (2 * t) * sizeof(btree_node *));
node->num = 0;
return node;
}
// desc:銷毀一個節點
void btree_destroy_node(btree_node *node)
{
assert(node);
free(node->childrens);
free(node->keys);
free(node);
}
//desc:建立一顆B樹
void btree_create(btree *T, int t)
{
T->t = t;
btree_node *x = btree_create_node(t, 1);
T->root = x;
}
//desc:分裂節點
//x:待分裂節點的父節點
//i: 分裂節點為x的第幾個孩子
void btree_split_child(btree *T, btree_node *x, int i)
{
int t = T->t;
btree_node *y = x->children[i]; // 待分裂節點
// 分裂後左半邊還是利用原來節點,右半邊開個新節點存
btree_node *z = btree_create_node(t, y->leaf);
z->num = t - 1; //分裂出的右半邊節點數量
int j = 0;
//将右半邊key值寫入到z節點
for(j = 0; j < t - 1; j++)
{
z->keys[j] = y->keys[j + t];
}
//非葉節點,處理孩子節點
if(y->leaf == 0)
{
for(j = 0;j < t; j++)
{
z->childrens[j] = y->children[j + t];
}
}
y->num = t-1; //分裂的節點key數量改變
//修改x節點(待分裂節點的父節點)
//節點上移時,x節點可能需要後移i+1位置後孩子和key
for(j = x->num; j >= i + 1; j--)
{
// x從x->num位置開始的孩子統一後移
x->childrens[j + 1] = x->childrens[j];
}
x->childrens[i + 1] = z;
// x節點從x->num位置開始的key統一後移
for(j = x->num - 1; j >= i; j--)
{
x->keys[j + 1] = x->keys[j];
}
x->keys[i] = y->keys[t - 1];
x->num += 1;
}
//desc:往不滿的節點裡插入
//x: 要插入的節點
//k: 要插入的關鍵字
void btree_insert_nonfull(btree *T, btree_node *x, KEY_TYPE k)
{
int i = x->num - 1;
if(x->leaf == 1) //葉子節點,可直接插入
{
// 節點内key升序
while(i >= 0 && x->keys[i] > k)
{
x->keys[i + 1] = x->keys[i];
i--;
}
x->keys[i + 1] = k;
x->num += 1;
}
else // 非葉子節點(插入節點必然在葉結點)
{
// 決定向x的哪個子節點遞歸下降
while(i >= 0 && x->keys[i] > k) i--;
// 遞歸降至一個滿子節點上,要分裂該子節點
if(x->childrens[i + 1]->num == (2 * (T->t)) - 1)
{
btree_split_child(T, x, i + 1);
// 确定向兩個孩子中哪個下降正确
if(k > x->keys[i + 1]) i++;
}
// 遞歸
btree_insert_nonfull(T, x->childrens[i + 1], k);
}
}
// desc:往樹T中插入鍵為key的節點
void btree_insert(btree *T, KEY_TYPE key)
{
btree_node *r = T->root;
//根節點若滿(key數量 == 2 * t - 1),分裂時,需要在頂上建立一個空節點(接受分裂後中間節點)
if(r->num == 2 * T->t -1)
{
btree_node *node = btree_create_node(T->t, 0);
T->root = node;
node->childrens[0] = r;//空根節點的第一個孩子設定為真正根節點
btree_split_child(T, node, 0);
int i = 0;
if(node->keys[0] < key) i++;
btree_insert_nonfull(T, node->childrens[i], key);
}
else
{
btree_insert_nonfull(T, r, key);
}
}
// 左右都是t - 1個key才合并
// 将child[idx], key[idx], child[idx + 1]合并為一個節點
void btree_merge(btree *T, btree_node *node, int idx)
{
btree_node *left = node->childrens[idx];
btree_node *right = node->childrens[idx + 1];
int i = 0;
// merge to left
left->keys[T->t - 1] = node->keys[idx];
// child[idx + 1]合并進去
for(i = 0;i < T->t - 1; i++)
{
left->keys[T->t + i] = right->keys[i];
}
if(!left->leaf) // 非葉情況,右邊節點孩子要并進去
{
for(i = 0; i < T->t; i++)
{
left->childrens[T->t + i] = right->childrens[i];
}
}
left->num += T->t;
btree_destroy_node(right);
// node 情況2c,即node非根,node的key減少1個
for(i = idx + 1; i < node->num; i++)
{
node->keys[i - 1] = node->keys[i];
node->childrens[i] = node->childrens[i + 1]
}
node->childrens[i + 1] = NULL;
node->num -= 1;
// 中間為根節點
if(node->num == 0)
{
T->root = left;
btree_destroy_node(node);
}
}
// 從以根為x的子樹的删除時必須保證,節點遞歸調用自身時x中key數量至少為t(比最小key數量多1)
// b樹删除key
// node -- key的祖先節點(不一定是根)
// key -- 待删除的key
void btree_delete_key(btree *T, btree_node *node, KEY_TYPE key)
{
// 先借位合并後删除
if(node == NULL) return;
int idx = 0, i;
// 在節點内找key
while (idx < node->num && key > node->keys[idx])
{
idx++;
}
// 在node裡找到待删的key
if(idx < node->num && node == node->keys[idx])
{
// key在葉結點中
if(node->leaf)
{
// node内所有key前移
for(i = idx; i < node->num - 1; i++ )
{
node->keys[i] = node->keys[i + 1];
}
node->keys[node->num - 1] = 0;
node->num--;
// root
if(node->num == 0)
{
free(node);
T->root = NULL;
}
return ;
}
// key在内節點, 且左邊孩子key數量大于t,可借位
else if(node->childrens[idx]->num >= T->t)
{
// 找節點左邊孩子最右key借位上移再删除這個孩子最右key
btree_node *left = node->childrens[idx];
node->keys[idx] = left->keys[left->num - 1];
btree_delete_key(T, left, left->keys[left->num - 1]);
}
// key在内節點, 且右邊孩子key數量大于t,可借位
else if(node->childrens[idx + 1]->num >= T->t)
{
btree_node *right = node->childrens[idx + 1];
node->keys[idx] = right->keys[0];
btree_delete_key(T, right, right->keys[0]);
}
// 兩邊孩子節點的key數量都為t - 1
else
{
// 合并左右孩子,放到下一層
btree_merge(T, node, idx);
btree_delete_key(T, node->childrens[idx], key);
}
}
else // 查找子節點
{
// key <= node->keys[idx]
btree_node *child = node->childrens[idx];
if(child == NULL)
{
printf("Cannot del key = %d\n", key);
return ;
}
// 孩子節點的key數量要 >=t ,否則要借位
if(child->num == T->t - 1)
{
btree_node *left = NULL;
btree_node *right = NULL;
// 擷取child的左右兄弟節點
if(idx - 1 >= 0)
{
left = node->childrens[idx - 1];
}
if(idx + 1 <= node->num)
{
right = node->childrens[idx + 1];
}
if((left && left->num >= T->t) || (right && right->num >= T->t))
{
int richR = 0;
if(right)
{
richR = 1;
}
if(left && right)
{
// 那邊孩子的key多
richR = (right->num > left->num) ? 1 : 0;
}
// 向右孩子借結點,父節點放到child節點上,然後向右child右兄弟借最左邊key放到父節點
if(right && right->num >= T->t && richR)
{
child->keys[child->num] = node->keys[idx];
child->childrens[child->num + 1] = right->childrens[0];
child->num++;
node->keys[idx] = right->keys[0];
for(i = 0; i < right->num - 1; i++)
{
right->keys[i] = right->keys[i + 1];
right->childrens[i] = right->keys[i + 1];
}
right->keys[right->num - 1] = 0;
right->childrens[right->num - 1] = right->childrens[right->num];
right->childrens[right->num] = NULL;
right->num--;
}
// 向左孩子借節點,用的是左孩子最右節點
else
{
// 把child的key和孩子節點指針數組先整體右移一位
for(i = child->num; i > 0; i--)
{
child->keys[i] = child->keys[i - 1];
child->childrens[i + 1] = child->childrens[i];
}
// 孩子數組調整一下
child->childrens[1] = child->childrens[0];
child->childrens[0] = left->childrens[left->num];
child->keys[0] = node->keys[idx - 1];
child->num ++;
node->key[idx - 1] = left->keys[left->num - 1];
left->keys[left->num - 1] = 0;
left->childrens[left->num] = NULL;
left->num--;
}
}
// 如果左右兄弟都沒得借,那就合并
else if((!left || (left->num == T->t - 1))
&& (!right || (right->num == T->t - 1)))
{
if(left && left->num == T->t - 1)
{
// 孩子,父親,孩子左兄弟
btree_merge(T, node, idx - 1)
}
else if(right && right->num == T->t - 1)
{
btree_merge(T, node, idx);
}
}
}
// 遞歸
btree_delete(T, child, key);
}
}
// 從樹T中删除key
int btree_delete(btree *T, KEY_TYPE key)
{
if(!T->root) return -1;
btree_delete_key(T, T->root, key);
return 0;
}
void btree_traverse(btree_node *x)
{
// bfs
int i = 0;
for(i = 0; i < x->num; i++)
{
if(x->leaf == 0)
{
btree_traverse(x->childrens[i]);
}
printf("%C", x->keys[i]);
}
if(x->leaf == 0) btree_traverse(x->childrens[i]);
}
void btree_print(btree *T, btree_node *node, int layer)
{
btree_node *p = node;
int i;
if(p)
{
printf("\nlayer = %d keynum = %d is_leaf = %d\n", leaf, p->num, p->leaf);
for(i = 0; i < node->num; i++)
{
printf("%c ", p->keys[i]);
}
printf("\n");
layer++;
for(i = 0; i <= p->num; i++)
{
if(p->childrens[i])
{
btree_print(T, p->childrens[i], layer);
}
}
}
else
{
printf("the tree is empty\n");
}
}
// 在node[low, high] 中查找key
int btree_bin_search(btree_node *node, int low, int high, KEY_TYPE key)
{
int mid;
if(low > high || low < 0 || high < 0)
{
return -1;
}
while(low <= high)
{
mid = (low + high) / 2;
if(key > node->keys[mid])
{
low = mid + 1;
}
else
{
high = mid - 1;
}
}
return low;
}
int main()
{
btree T = {0};
btree_create(&T, 3);
srand(48);
int i = 0;
char key[26] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
for(i = 0; i < 26; i++)
{
printf("%c ", key[i]);
btree_insert(&T, key[i]);
}
// 從B樹T第0層開始列印
btree_print(&T, T.root, 0);
for(i = 0; i < 26; i++)
{
printf("----------------------------------\n");
btree_delete(&T, key[i]);
btree_print(&T, T.root, 0);
}
}