怎样用b+树实现固定长度字符串的查找,请用C语言写一个示例代码。
时间: 2024-03-24 12:37:26 浏览: 19
B+树是一种常用的索引结构,适用于范围查询等场景。下面是一个使用B+树实现固定长度字符串查找的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_KEY_SIZE 256
#define MAX_VALUE_SIZE 1024
#define MAX_CHILDREN_NUMBER 100
typedef struct BPTreeNode {
char key[MAX_KEY_SIZE];
char value[MAX_VALUE_SIZE];
struct BPTreeNode* children[MAX_CHILDREN_NUMBER];
int children_number;
} BPTreeNode;
typedef struct BPTree {
BPTreeNode* root;
int key_size;
} BPTree;
BPTreeNode* create_node(int key_size) {
BPTreeNode* node = (BPTreeNode*)malloc(sizeof(BPTreeNode));
if (node != NULL) {
memset(node->key, 0, sizeof(char) * key_size);
memset(node->value, 0, sizeof(node->value));
for (int i = 0; i < MAX_CHILDREN_NUMBER; i++) {
node->children[i] = NULL;
}
node->children_number = 0;
}
return node;
}
void insert(BPTree* tree, char* key, char* value) {
BPTreeNode* node = tree->root;
if (node == NULL) {
node = create_node(tree->key_size);
strncpy(node->key, key, tree->key_size);
strncpy(node->value, value, sizeof(node->value));
tree->root = node;
return;
}
while (node->children[0] != NULL) {
int i;
for (i = 0; i < node->children_number; i++) {
if (strcmp(node->children[i]->key, key) > 0) {
break;
}
}
node = node->children[i];
}
int i;
for (i = 0; i < node->children_number; i++) {
if (strcmp(node->children[i]->key, key) == 0) {
strncpy(node->children[i]->value, value, sizeof(node->value));
return;
}
if (strcmp(node->children[i]->key, key) > 0) {
break;
}
}
BPTreeNode* new_node = create_node(tree->key_size);
strncpy(new_node->key, key, tree->key_size);
strncpy(new_node->value, value, sizeof(new_node->value));
for (int j = node->children_number; j > i; j--) {
node->children[j] = node->children[j-1];
}
node->children[i] = new_node;
node->children_number++;
}
char* search(BPTree* tree, char* key) {
BPTreeNode* node = tree->root;
if (node == NULL) {
return NULL;
}
while (node->children[0] != NULL) {
int i;
for (i = 0; i < node->children_number; i++) {
if (strcmp(node->children[i]->key, key) > 0) {
break;
}
}
node = node->children[i];
}
int i;
for (i = 0; i < node->children_number; i++) {
if (strcmp(node->children[i]->key, key) == 0) {
return node->children[i]->value;
}
if (strcmp(node->children[i]->key, key) > 0) {
break;
}
}
return NULL;
}
int main() {
BPTree* tree = (BPTree*)malloc(sizeof(BPTree));
tree->root = NULL;
tree->key_size = 10;
insert(tree, "hello", "world");
insert(tree, "world", "hello");
char* value = search(tree, "hello");
printf("value: %s\n", value);
value = search(tree, "world");
printf("value: %s\n", value);
value = search(tree, "foo");
printf("value: %s\n", value); // NULL
return 0;
}
```
这个示例代码中,我们使用了一个结构体`BPTreeNode`来表示B+树中的一个节点,其中包含了键值对以及子节点的信息。`BPTree`结构体则表示整棵B+树,包含了根节点以及键值的长度等信息。在`insert`函数中,我们首先找到应该插入的叶子节点,如果该节点已经存在相同的键,则更新其对应的值。否则,我们在叶子节点上插入一个新的键值对,并按照键的大小顺序将子节点链接起来。在`search`函数中,我们也是通过遍历B+树来找到对应的叶子节点,然后在叶子节点中查找是否存在对应的键值对。