怎样用b+树实现固定长度字符串的查找,请给出C语言实现的代码。
时间: 2024-03-24 15:39:00 浏览: 17
B+树是一种常用的数据结构,用于在大量数据中进行高效的查找和插入操作。它的主要特点是,将数据按照一定规则分层存储,每一层都有一个索引节点和若干数据节点。这样,可以快速定位到需要查找的数据所在的位置,从而提高查找效率。
在使用B+树实现固定长度字符串的查找时,我们可以将字符串看作是一个固定长度的字符数组,按照字典序进行排序,然后将其作为关键字插入到B+树中。具体实现如下:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_KEY_LEN 32 // 字符串最大长度
#define M 3 // B+树的阶数
// B+树的节点结构
typedef struct node {
int is_leaf; // 是否为叶子节点
int num_keys; // 关键字数量
char keys[M-1][MAX_KEY_LEN]; // 关键字数组
struct node *child[M]; // 子节点指针数组
} node;
// 创建一个新节点
node* create_node() {
node *new_node = (node*) malloc(sizeof(node));
new_node->is_leaf = 0;
new_node->num_keys = 0;
memset(new_node->keys, 0, sizeof(new_node->keys));
memset(new_node->child, 0, sizeof(new_node->child));
return new_node;
}
// 在叶子节点中插入一个关键字
void insert_into_leaf(node *leaf, char *key) {
int i, j, insert_pos;
insert_pos = 0;
while (insert_pos < leaf->num_keys && strcmp(key, leaf->keys[insert_pos]) > 0) {
insert_pos++;
}
for (i = leaf->num_keys; i > insert_pos; i--) {
strcpy(leaf->keys[i], leaf->keys[i-1]);
}
strcpy(leaf->keys[insert_pos], key);
leaf->num_keys++;
}
// 在非叶子节点中插入一个关键字
void insert_into_node(node *parent, int pos, char *key, node *right_child) {
int i, j;
for (i = parent->num_keys; i > pos; i--) {
strcpy(parent->keys[i], parent->keys[i-1]);
parent->child[i+1] = parent->child[i];
}
strcpy(parent->keys[pos], key);
parent->child[pos+1] = right_child;
parent->num_keys++;
}
// 分裂叶子节点
void split_leaf(node *leaf, node *parent, int pos) {
int i, j, split_pos;
node *new_leaf = create_node();
split_pos = leaf->num_keys / 2;
for (i = split_pos, j = 0; i < leaf->num_keys; i++, j++) {
strcpy(new_leaf->keys[j], leaf->keys[i]);
new_leaf->num_keys++;
}
leaf->num_keys = split_pos;
new_leaf->is_leaf = 1;
new_leaf->child[M-1] = leaf->child[M-1];
leaf->child[M-1] = new_leaf;
strcpy(new_leaf->keys[new_leaf->num_keys], leaf->keys[leaf->num_keys-1]);
new_leaf->num_keys++;
insert_into_node(parent, pos, new_leaf->keys[0], new_leaf);
}
// 分裂非叶子节点
void split_node(node *node, node *parent, int pos) {
int i, j, split_pos;
node *new_node = create_node();
split_pos = node->num_keys / 2;
for (i = split_pos+1, j = 0; i < node->num_keys; i++, j++) {
strcpy(new_node->keys[j], node->keys[i]);
new_node->child[j] = node->child[i];
node->child[i] = NULL;
new_node->num_keys++;
node->num_keys--;
}
new_node->child[j] = node->child[i];
node->child[i] = NULL;
node->num_keys--;
insert_into_node(parent, pos, node->keys[split_pos], new_node);
}
// 插入一个关键字到B+树中
void insert(node **root, char *key) {
int i, j, insert_pos, split_pos;
node *leaf, *parent, *current;
current = *root;
parent = NULL;
if (current == NULL) {
leaf = create_node();
leaf->is_leaf = 1;
strcpy(leaf->keys[0], key);
leaf->num_keys++;
*root = leaf;
return;
}
while (!current->is_leaf) {
parent = current;
insert_pos = 0;
while (insert_pos < current->num_keys && strcmp(key, current->keys[insert_pos]) > 0) {
insert_pos++;
}
current = current->child[insert_pos];
}
insert_into_leaf(current, key);
if (current->num_keys == M-1) {
split_leaf(current, parent, insert_pos);
}
while (parent != NULL) {
current = parent;
parent = current->child[M-1];
for (i = 0; i < current->num_keys && parent != current->child[i]; i++);
if (current->child[i]->num_keys == M-1) {
split_node(current->child[i], current, i);
}
}
}
// 在B+树中查找一个关键字
int search(node *root, char *key) {
int i, result = 0;
node *current = root;
while (current != NULL) {
for (i = 0; i < current->num_keys && strcmp(key, current->keys[i]) >= 0; i++) {
if (strcmp(key, current->keys[i]) == 0) {
result = 1;
break;
}
}
if (result) {
break;
}
current = current->child[i];
}
return result;
}
int main() {
node *root = NULL;
char keys[][MAX_KEY_LEN] = {"abc", "def", "ghi", "jkl", "mno", "pqr", "stu", "vwx", "yz"};
int i;
for (i = 0; i < sizeof(keys)/sizeof(keys[0]); i++) {
insert(&root, keys[i]);
}
printf("%d\n", search(root, "abc")); // 1
printf("%d\n", search(root, "xyz")); // 0
return 0;
}
```
以上是一个简单的B+树实现固定长度字符串的查找的代码,其中M是B+树的阶数,MAX_KEY_LEN是字符串的最大长度,可以根据实际情况进行调整。