B-Tree 学习

算法导论第18章 B树
与其他树的结构不同的是 B数是多叉而不是二叉树而且分叉因子很大
一般使用于数据库针对需要硬盘IO的情况而使用可以降低磁盘IO
B树的一个节点是以磁盘的页面为单位，而不是数据内容为单位一般一个节点等于一个完整的磁盘页

以下B树性质是本人理解具体定义可查阅算法导论18章节
除了根节点以外所有节点拥有T-1个到 2T-1个关键字
关键字升序或者降序排列
节点拥有T个到2T个指针指向子节点定义为子节点
若节点仅拥有关键字而无指针为叶子节点在树的最下端
T=2时候树拥有2、3或者4个子节点成为2-3-4树

以下为我学习的一个简单代码确定了B树的结构和创建、查找功能打印节点数值功能。

增删功能比较麻烦，后继增加

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// 1213.cpp : 定义控制台应用程序的入口点。
//
 
#include "stdafx.h"
#include <iostream>
#include <list>
#include <vector>
#include <assert.h>
using namespace std;
 
#define t 2;
 
struct MyB_Tree {
    size_t  keySize_;
    bool    isLeaf_;
    std::vector<size_t>          keys_;
    std::vector<MyB_Tree*>    subTrees_;
    MyB_Tree() {
        keySize_ = 0;
        isLeaf_ = true;
    }
};
 
struct SearchResult {
    MyB_Tree*   pBTree_;
    size_t      keyNum_;
    SearchResult() {
        pBTree_ = NULL;
        keyNum_ = 0;
    }
    SearchResult(MyB_Tree* pBTree, size_t keyNum) {
        pBTree_ = pBTree;
        keyNum_ = keyNum;
    }
};
 
MyB_Tree* CreateB_TreeNode() {
    MyB_Tree* pBTree = new MyB_Tree();
    return pBTree;
}
 
bool BTreeeSearch(MyB_Tree* pBTree, size_t value, SearchResult& result) {
    bool ret = false;
    size_t i = 0;
    while (i <pBTree->keySize_ && value >  pBTree->keys_[i]) {
        i++;
    }
    if (i <pBTree->keySize_ && value == pBTree->keys_[i])
    {
        result.pBTree_ = pBTree;
        result.keyNum_ = i;
        ret = true;
        return ret;
    }
    if (pBTree->isLeaf_) {
        return ret;
    }
    else {
        return BTreeeSearch(pBTree->subTrees_[i], value, result);
    }
}
 
void PrintTree(MyB_Tree* p) {
    std::cout << "//==========================\nstart print keys : ";
    for (int i = 0; i<p->keySize_; i++) {
        std::cout << p->keys_[i] << " ";
    }
 
    std::cout << "\n//==========================" << std::endl;
    if (!p->isLeaf_) {
        for (int i = 0; i <= p->keySize_; i++)
        {
            PrintTree(p->subTrees_[i]);
        }
    }
}
 
 
 
 
 
int main(int argc, char *argv[])
{
    MyB_Tree* root = CreateB_TreeNode();
    MyB_Tree* subright = CreateB_TreeNode();
    MyB_Tree* subleft = CreateB_TreeNode();
 
    root->keySize_ = 1;
    root->keys_.push_back(20);
 
    subleft->keySize_ = 2;
    subleft->keys_.push_back(10);
    subleft->keys_.push_back(19);
 
    subright->keySize_ = 3;
    subright->keys_.push_back(21);
    subright->keys_.push_back(25);
    subright->keys_.push_back(30);
 
 
    root->isLeaf_ = false;
    root->subTrees_.push_back(subleft);
    root->subTrees_.push_back(subright);
 
    PrintTree(root);
 
    SearchResult result;
    assert(BTreeeSearch(root, 33, result) == false);
    assert(BTreeeSearch(root, 25, result) == true);
    assert(result.pBTree_ == subright);
    assert(result.keyNum_ == 1);
 
    std::cout << "finished " << std::endl;
    return 0;
}