B-trees are balanced search trees designed to work well on disks or other direct access
secondary storage devices.
B-trees are similar to red-black trees in that every n-node B-tree has height O.lg n/.
The exact height of a B-tree can be considerably less than that of a red-black tree,
however, because its branching factor, and hence the base of the logarithm that
expresses its height, can be much larger. Therefore, we can also use B-trees to
implement many dynamic-set operations in time O(lg n).
it is a designed to work on a disk data structures (differently from data structures
designed to work in main random-access memory.)
In order to amortize the time spent waiting for mechanical movements, disks
access not just one item but several at a time. Information is divided into a number
of equal-sized pages of bits that appear consecutively within tracks, and each disk
read or write is of one or more entire pages. For a typical disk, a page might be 211
to 214 bytes in length. Once the read/write head is positioned correctly and the disk
has rotated to the beginning of the desired page, reading or writing a magnetic disk
is entirely electronic (aside from the rotation of the disk), and the disk can quickly
read or write large amounts of data.
If the object is currently in the computer’s main memory, then we can refer
to the attributes of the object as usual: x:key, for example. If the object referred to
by x resides on disk, however, then we must perform the operation DISK-READ.x/
to read object x into main memory before we can refer to its attributes. (We assume
that if x is already in main memory, then DISK-READ.x/ requires no disk
accesses; it is a “no-op.”)
we typically want each of these operations to read or write as much information as
possible. Thus, a B-tree node is usually as large as a whole disk page, and this size
limits the number of children a B-tree node can have.
In a typical B-tree application, the amount of data handled is so large that all
the data do not fit into main memory at once. The B-tree algorithms copy selected
pages from disk into main memory as needed and write back onto disk the pages
that have changed. B-tree algorithms keep only a constant number of pages in
main memory at any time; thus, the size of main memory does not limit the size of
B-trees that can be handled.
Searching a B-tree
B-TREE-SEARCH is a straightforward generalization of the TREE-SEARCH procedure
defined for binary search trees. B-TREE-SEARCH takes as input a pointer
to the root node x of a subtree and a key k to be searched for in that subtree. The
top-level call is thus of the form B-TREE-SEARCH.T:root; k/. If k is in the B-tree,
B-TREE-SEARCH returns the ordered pair .y; i / consisting of a node y and an
index i such that y:keyi D k. Otherwise, the procedure returns NIL.
Inserting a key into a B-tree
As with binary search trees, we search for the leaf position
at which to insert the new key. With a B-tree, however, we cannot simply create
a new leaf node and insert it, as the resulting tree would fail to be a valid B-tree.
Instead, we insert the new key into an existing leaf node. Since we cannot insert a
key into a leaf node that is full, we introduce an operation that splits a full node y
(having 2t 1 keys) around its median key y:keyt into two nodes having only t 1
keys each. The median key moves up into y’s parent to identify the dividing point
between the two new trees. But if y’s parent is also full, we must split it before we
can insert the new key, and thus we could end up splitting full nodes all the way up
the tree.
As with a binary search tree, we can insert a key into a B-tree in a single pass
down the tree from the root to a leaf. To do so, we do not wait to find out whether
we will actually need to split a full node in order to do the insertion. Instead, as we
travel down the tree searching for the position where the new key belongs, we split
each full node we come to along the way (including the leaf itself). Thus whenever
we want to split a full node y, we are assured that its parent is not full.
Splitting a node in a B-tree
Deleting a key from a B-tree
when we delete a
key from an internal node, we will have to rearrange the node’s children. As in
insertion, we must guard against deletion producing a tree whose structure violates
the B-tree properties. Just as we had to ensure that a node didn’t get too big due to
insertion, we must ensure that a node doesn’t get too small during deletion (except
that the root is allowed to have fewer than the minimum number t 1 of keys).
Just as a simple insertion algorithm might have to back up if a node on the path
to where the key was to be inserted was full, a simple approach to deletion might
have to back up if a node (other than the root) along the path to where the key is to
be deleted has the minimum number of keys.
We sketch how deletion works instead of presenting the pseudocode. Figure 18.8
illustrates the various cases of deleting keys from a B-tree.
1. If the key k is in node x and x is a leaf, delete the key k from x.
2. If the key k is in node x and x is an internal node, do the following:
a. If the child y that precedes k in node x has at least t keys, then find the
predecessor k0 of k in the subtree rooted at y. Recursively delete k0, and
replace k by k0 in x. (We can find k0 and delete it in a single downward
pass.)
b. If y has fewer than t keys, then, symmetrically, examine the child ´ that
follows k in node x. If ´ has at least t keys, then find the successor k0 of k in
the subtree rooted at ´. Recursively delete k0, and replace k by k0 in x. (We
can find k0 and delete it in a single downward pass.)
c. Otherwise, if both y and ´ have only t 1 keys, merge k and all of ´ into y,
so that x loses both k and the pointer to ´, and y now contains 2t 1 keys.
Then free ´ and recursively delete k from y.
3. If the key k is not present in internal node x, determine the root x:ci of the
appropriate subtree that must contain k, if k is in the tree at all. If x:ci has
only t 1 keys, execute step 3a or 3b as necessary to guarantee that we descend
to a node containing at least t keys. Then finish by recursing on the appropriate
child of x.
a. If x:ci has only t 1 keys but has an immediate sibling with at least t keys,
give x:ci an extra key by moving a key from x down into x:ci, moving a
key from x:ci ’s immediate left or right sibling up into x, and moving the
appropriate child pointer from the sibling into x:ci .
b. If x:ci and both of x:ci ’s immediate siblings have t 1 keys, merge x:ci
with one sibling, which involves moving a key from x down into the new
merged node to become the median key for that node.
Since most of the keys in a B-tree are in the leaves, we may expect that in
practice, deletion operations are most often used to delete keys from leaves. The
B-TREE-DELETE procedure then acts in one downward pass through the tree,
without having to back up. When deleting a key in an internal node, however,
the procedure makes a downward pass through the tree but may have to return to
the node from which the key was deleted to replace the key with its predecessor or
successor (cases 2a and 2b)
code
#ifndef _BTREE_
#define _BTREE_
#define m 3 /*m 路Btree*/
#define L 3 /*B+ Tree 元素节点最大长度*/
#include <iostream>
#include <math.h>
#include <stack>
using namespace std; class TreeNode
{
friend class Btree;
friend class Result;
friend class BPlusTree;
public:
TreeNode()/*用于区分是否为BPlus 树的叶子节点 即数据节点*/
{
keynum=0;/*是数据节点*/
}
TreeNode(TreeNode* p1,int k,TreeNode *p2)/*构造根节点*/
{
keynum=1;
key[1]=k;
parent=0;
fill(ptr,ptr+m+1,(TreeNode*)0);
ptr[0]=p1;
ptr[1]=p2;
/* 设置子树的父节点*/
if (p1)
p1->parent=this;
if(p2)
p2->parent=this;
}
TreeNode(TreeNode* p,int *keyarry,TreeNode**ptrarry)/*分裂的新节点*/
{
parent=p;
fill(ptr,ptr+m+1,(TreeNode*)0);
int temp=ceil(m/2.0);//向上取整
ptr[0]=ptrarry[temp];
if(ptr[0])/*分裂后节点的父节点改变*/
ptr[0]->parent=this;
for (int i=1;i+temp<=m;i++)
{
key[i]=keyarry[temp+i];
ptr[i]=ptrarry[temp+i];
if (ptr[i])/*分裂后节点的父节点改变*/
ptr[i]->parent=this;
keyarry[temp+i]=0;
ptrarry[temp+i]=0;
}
keyarry[temp]=0;
ptrarry[temp]=0;
keynum=m-temp;
}
protected:
int keynum;/*关键字个数 keynum <=m-1*/
TreeNode *parent;/*父节点指针*/
TreeNode *ptr[m+1];/*子树指针 0...m */
int key[m+1];/*1...m 多一个单元可以保证当溢出时也可直接插入 之后在进行分裂*/
}; class Result
{
friend class Btree;
public:
Result(TreeNode*p=0,int i=0,bool r=0)
{
ResultPtr=p;
index=i;
Resultflag=r;
}
TreeNode * ResultPtr;
int index;
bool Resultflag;
};
class Btree
{
public:
Btree()
{
root=0;
}
void InsertBtree(int k);
Result Find(int k);
void DeleteBtree(int k);
void Insert(int k,TreeNode* node,TreeNode* p);/*关键字：k 该关键字k的右子树指针 插入节点a */
protected:
void BorrowOrCombine(TreeNode *a,int i,int type,stack<int> &s);/*待处理关键字是a 节点的 i
type 标志此次操作的前一次是 对其左 -1 右 1 无0 孩子进行操作*/
//void Insert(int k,TreeNode* node,TreeNode* p);/*关键字：k 该关键字k的右子树指针 插入节点a */
TreeNode *root;
}; /*B+Tree */
class DataNode: public TreeNode
{
friend class BPlusTree;
public:
DataNode(int k)/*构造第一个数据节点*/
{
data[1]=k;
parent=0;
pre=next=0;
datanum=1;
};
DataNode(TreeNode* Parent,DataNode*Pre,DataNode* Next,int *dataArray)/*分裂数据节点*/
{
parent=Parent;
pre=Pre;
next=Next;
int temp=ceil(L/2.0);
// copy(dataArray+1+temp,dataArray+L+1,data+1);
for (int i=1;i<=L+1-temp;i++)
{
data[i]=dataArray[i+temp];
dataArray[i+temp]=0;
}
datanum=L+1-temp;
Pre->datanum=temp;
}
private:
DataNode *pre;
DataNode *next;
int data[L+2];
int datanum;
};
class BPlusTree :public Btree
{
public:
BPlusTree()
{
root=0;
header=0;
}
void InsertBplustree(int k);/*插入关键字*/
void InsertData(int k,DataNode* dn);
void DeleteBPlustree(int k);/*删除关键字k*/
private:
DataNode* header;
};
#include "Btree.h"
#include <iostream>
#include <math.h>
#include <stack>
using namespace std;
void Btree::InsertBtree(int k)
{
if (!root)
{
root=new TreeNode(0,k,0);
return ;
}
TreeNode *a=root;/*当前节点*/
int i=1;/*k关节字 要插入节点a 的位置索引*/
/*找到插入节点*/
while(a)
{
i=1;
/*在a 中找到第一个比关键字k大的关键字的位置 i */
while(i<=a->keynum)
{
if (k<=a->key[i])
break;
else
i++;
}
/* 判断是否继续向下 还是已经到达子节点 */
if (!a->ptr[i-1])/* 已是叶子节点无需向下 直接插入 */
break;
else/*不是叶子节点*/
a=a->ptr[i-1];
}
if (a->key[i]==k)/*该关键字节点已存在 */
return ;
Insert(k,0,a);/*在叶子节点中插入关键字k*/
}
void Btree::Insert(int k,TreeNode* node,TreeNode* a)/*关键字：k 该关键字k的右子树指针 插入节点a */
{
int i=1;
/*在a 中找到第一个比关键字k大的关键字的位置 i */
while(i<=a->keynum)
{
if (k<=a->key[i])
break;
else
i++;
}
/*插入节点为 a 索引为 i */
for (int j=a->keynum;j>=i;j--)/*向后移动以便插入新关键字*/
{
a->key[j+1]=a->key[j];/* 关键字*/
a->ptr[j+1]=a->ptr[j];/*子树指针*/
}
a->key[i]=k;
a->ptr[i]=node;
a->keynum++;
if (a->keynum<=m-1) return;
else
{/*分裂节点然后插入父节点 |1 2 3 ...|ceil(m)(向上取整)|... m| */
int midkey=a->key[(int)ceil(m/2.0)];/*中间关键字及 NewNode 要插入父节点*/
TreeNode* NewNode=new TreeNode(a->parent,a->key,a->ptr);/*和a同parent*/
/*
for (int i=0;i<=NewNode->keynum;i++)
{
if (NewNode->ptr[i])
NewNode->ptr[i]->parent=NewNode;
}*/
a->keynum=m-ceil(m/2.0);
TreeNode * tempa=a;/*记录当前节点*/
a=a->parent;/*父节点*/
if (!a)/*无父节点*/
{
TreeNode *NewRoot=new TreeNode(tempa,midkey,NewNode);
tempa->parent=NewRoot;
NewNode->parent=NewRoot;
root=NewRoot;
return;
}
else
Insert(midkey,NewNode,a);
}
}
Result Btree::Find(int k)
{
if (!root)
{
cout<<"the tree is null !"<<endl;
return Result(0,0,0);
}
TreeNode* a=root;
int i=1;
while(a)
{
i=1;
while(i<=a->keynum)
{
if (k<=a->key[i])
{
break;
}
else
{
i++;
}
}
if (k==a->key[i])
{
return Result(a,i,1);
}
else
{
if (!a->ptr[i-1])
{ return Result(a,i,0);
}
else
{
a=a->ptr[i-1];
}
}
}
}
void Btree::DeleteBtree(int k)
{
if (!root)
{
cout<<"The tree is null !"<<endl;
return;
}
/*转化为删除叶子节点中的关键字 找其右子树的最小关键字*/
stack<int> s;/*记录路径上的 所有 index */
TreeNode *delnode=root;//待删除关键字k所在节点
int i=1; while (delnode&&delnode->keynum)/*delnode->keynum ==0 是对B+树而言*/
{
i=1;
while(i<=delnode->keynum)
{
if (k<=delnode->key[i])
{
break;
}
else
{
i++;
}
}
if (k==delnode->key[i])
{
break;/*找到了*/
}
else
{
if (delnode->ptr[i-1]==0)
{
/*无此关键字*/
cout<<"no this key :"<<k<<endl;
return ;
}
else
{
/*向下一层*/
delnode=delnode->ptr[i-1];
s.push(i-1);/*通过该索引的指针向下一层查找*/
}
}
}
/* delnode i parent可以提供回去的路 */
TreeNode *p=delnode;/*当前节点*/
if (delnode->ptr[i]&&delnode->ptr[i]->keynum)/*delnode 不是叶子节点*//*B+tree 的元素节点*/
{ s.push(i);
p=delnode->ptr[i]; while(p->ptr[0]&&p->ptr[0]->keynum)/* p到达delnode 的右子树中最小关键字节点*/
{
p=p->ptr[0];
if (!p->ptr[0]->keynum)
break;
s.push(0);
}
}
if (p!=delnode)
{
/*将删除操作到对叶子节点的关键字的删除*/
delnode->key[i]=p->key[1];
i=1;
}
/* p, i 删除关键字由delnode i 转换为 p i */
BorrowOrCombine(p,i,0,s);
}
void Btree::BorrowOrCombine(TreeNode *a,int i,int type,stack<int> &s)/*待处理关键字是a 节点的 i
type 标志此次操作的前一次是 对其左 -1 右 1 无0 孩子进行操作 即这是对叶子节点的操作*/
{
if (a==root&&root->keynum==1)
{ TreeNode * oldroot=root;
if (type==-1)
{
if (root->ptr[i])
root=root->ptr[i];
else
root=0;
}
else if (type==1)
{
if (root->ptr[i-1])
root=root->ptr[i-1];
else
root=0;
}
else/*不是由下层传递而来*/
{
root=0;
}
if(root)
root->parent=0;
delete oldroot; return;
}
int minnum=ceil(m/2.0)-1;
TreeNode *la,*ra;/*a 的左右兄弟节点*/
// if (!a->ptr[0])/*a 为叶子节点*/
// {
TreeNode *pflag=a->ptr[i-1];/*对B+树 判断哪个元素节点被合并掉了 指针为0*/ if (a->keynum>minnum||a==root)
{
for (int j=i;j<a->keynum;j++)
{
a->key[j]=a->key[j+1];
if (type==-1)
{
a->ptr[j-1]=a->ptr[j];
}
else if (type==1)
{
a->ptr[j]=a->ptr[j+1];
}
else
{
/*这是对叶子节点的操作 B+树 而言*/
if (pflag)
{
a->ptr[j]=a->ptr[j+1];
}
else
{
a->ptr[j-1]=a->ptr[j];
}
}
}
if (!type&&!pflag)
{
a->ptr[j-1]=a->ptr[j];
}
if (type==-1)
{
a->ptr[j-1]=a->ptr[j];
}
a->key[j]=0;
a->ptr[j]=0;
a->keynum--;
return;
}
else
{/* aa->keynum=minnum */
int index=s.top();
s.pop();
/*能借则借 借优先*/
if (index)/*有左兄弟*/
{
la=a->parent->ptr[index-1];
if (la->keynum>minnum)/*左兄弟关键字足够多可以借*/
{
/* 从左兄弟借 */
/*向后移动覆盖 i */
for (int j=i;j>1;j--)
{
a->key[j]=a->key[j-1];
if (type==-1)
{
a->ptr[j-2]=a->ptr[j-1];
}
else if (type==1)
{
a->ptr[j-1]=a->ptr[j];
}
else
{
if (pflag)
{
a->ptr[j-1]=a->ptr[j];
}
else
{
a->ptr[j-2]=a->ptr[j-1];
}
}
}
if (!type&&pflag)
{
a->ptr[j-1]=a->ptr[j];
}
if (type==1)
{
a->ptr[j-1]=a->ptr[j];
}
a->key[j]=a->parent->key[index];
a->ptr[0]=la->ptr[la->keynum];/*左兄弟的最右子树*/
/*父节点改变*/
la->ptr[la->keynum]->parent=a;
a->parent->key[index]=la->key[la->keynum]; la->key[la->keynum]=0;
la->ptr[la->keynum]=0;
la->keynum--; return;
}
}
if (index<a->keynum)/*有右兄弟index<=a->keynum*/
{ ra=a->parent->ptr[index+1]; if (ra->keynum>minnum)/*右兄弟关键字足够多可以借*/
{
/* 从右兄弟借 */
/*向前移动覆盖 i */
for (int j=i;j<a->keynum;j++)
{
a->key[j]=a->key[j+1];
if (type==-1)
{
a->ptr[j-1]=a->ptr[j];
}
else if (type==1)
{
a->ptr[j]=a->ptr[j+1];
}
else
{
if (pflag)
{
a->ptr[j]=a->ptr[j+1];
}
else
{
a->ptr[j-1]=a->ptr[j];
}
}
}
if (!type&&!pflag)
{
a->ptr[j-1]=a->ptr[j];
}
if (type==-1)
{
a->ptr[j-1]=a->ptr[j];
}
a->key[j]=a->parent->key[index+1];
a->ptr[j]=ra->ptr[0];/*右兄弟的最左子树*/
if (ra->ptr[0]) /*叶子节点的 -》ptr【0】==0*/
ra->ptr[0]->parent=a;
a->parent->key[index+1]=ra->key[1];
/*右兄弟关键字去头 前移*/
for (int t=1;t<ra->keynum;t++)
{
ra->ptr[t-1]=ra->ptr[t];
ra->key[t]=ra->key[t+1];
}
/*t= ra->keynum */
ra->ptr[t-1]=ra->ptr[t];
ra->key[t]=0;
ra->ptr[t]=0;
ra->keynum--;
return;
}
}
/*合并可能会使 不完善节点向上传递*/
if (index)/*有左兄弟*/
{
la=a->parent->ptr[index-1];
if (la->keynum==minnum)/*左兄弟关键字不够多*/
{
/* 合并到左兄弟 */ la->key[la->keynum+1]=a->parent->key[index];
/*a 中的关键字填充到其左兄弟中 0 1 2 .... i-1 | i | i+1 ...... kyenum */ for (int l=1;l<=i-1;l++)
{
la->key[la->keynum+l+1]=a->key[l];
la->ptr[la->keynum+l]=a->ptr[l-1];
/*子树的父节点改变*/
if(a->ptr[l-1])
a->ptr[l-1]->parent=la;
} if (type==-1)
{
la->ptr[la->keynum+l]=a->ptr[l];
if(a->ptr[l])
a->ptr[l]->parent=la;
}
else if(type==1)
{
la->ptr[la->keynum+l]=a->ptr[l-1];
if(a->ptr[l-1])
a->ptr[l-1]->parent=la;
}
else
{
if (pflag)
{
la->ptr[la->keynum+l]=a->ptr[l-1];
if(a->ptr[l-1])
a->ptr[l-1]->parent=la;
}
else
{
la->ptr[la->keynum+l]=a->ptr[l];
if(a->ptr[l])
a->ptr[l]->parent=la;
}
} for (l=i;l<a->keynum;l++)
{
la->key[la->keynum+l+1]=a->key[l+1];
la->ptr[la->keynum+l+1]=a->ptr[l+1];
if(a->ptr[l+1])
a->ptr[l+1]->parent=la;
}
la->keynum=m-1;
TreeNode *tempp=a->parent;
tempp->ptr[index]=0;
delete a;
BorrowOrCombine(tempp,index,1,s);
return;
}
}
if (index<a->keynum)/*有右兄弟index<=a->keynum*/
{
ra=a->parent->ptr[index+1];
if (ra->keynum==minnum)/*右兄弟关键字不够多*/
{
/*合并到右兄弟 */
/* 右兄弟关键字右移 让出合并位置*/
for (int k=ra->keynum;k>0;k--)
{
ra->key[k+a->keynum]=ra->key[k];
ra->ptr[k+a->keynum]=ra->ptr[k];
}
ra->ptr[a->keynum]=ra->ptr[0]; ra->key[a->keynum]=a->parent->key[index+1];
/*a 中的关键字填充到其右兄弟中 0 1 2 .... i-1 | i | i+1 ...... kyenum */ for (int l=1;l<=i-1;l++)
{
ra->ptr[l-1]=a->ptr[l-1];
ra->key[l]=a->key[l];
/*子树的父节点改变*/
if(a->ptr[l-1])
a->ptr[l-1]->parent=ra;
}
if (type==-1)
{
ra->ptr[l-1]=a->ptr[l];
if(a->ptr[l])
a->ptr[l]->parent=ra;
}
else if (type==1)
{
ra->ptr[l-1]=a->ptr[l-1];
if(a->ptr[l-1])
a->ptr[l-1]->parent=ra;
}
else
{
if (pflag)
{
ra->ptr[l-1]=a->ptr[l-1];
if(a->ptr[l-1])
a->ptr[l-1]->parent=ra;
}
else
{
ra->ptr[l-1]=a->ptr[l];
if(a->ptr[l])
a->ptr[l]->parent=ra;
}
}
/*叶子节点无所谓 都是 0 */
for (l=i+1; l<=a->keynum;l++)
{
ra->key[l]=a->key[l];
ra->ptr[l]=a->ptr[l];
if(a->ptr[l])
a->ptr[l]->parent=ra;
}
ra->keynum=m-1;
TreeNode *tempp=a->parent;
tempp->ptr[index]=0;
delete a;/*删除节点a */
/**/ BorrowOrCombine(tempp,index+1,-1,s);
return;
}
}
}
}
/*
* **************************************************************
* B+tree
*/ void BPlusTree::InsertBplustree(int k)
{
if (!root)
{
if (!header)
{
header=new DataNode(k);
}
else
{
InsertData(k,header);
}
return;
}
/*find the data node where to insert the key */
TreeNode *inode=root; while(inode->keynum)/*不是叶子节点就继续向下*/
{
int i=1;
while(i<inode->keynum)
{
if (k>inode->key[i])
{
i++;
}
else
break;
} if (k<inode->key[i])
{
/*左子树*/
inode=inode->ptr[i-1];
}
else
{
/*右子树*/
inode=inode->ptr[i];
}
}
/*找到相应的叶子节点 inode */
InsertData(k,(DataNode*)inode); }
void BPlusTree::InsertData(int k,DataNode* dn)
{
int i=1;
while (i<=dn->datanum)
{
if (k>dn->data[i])
{
i++;
}
else
break;
}
/**/
if (k==dn->data[i])
{
/*关键字已存在*/
return ;
}
else
{
/*数据后移以便插入关键字*/
for (int j=L;j>=i;j--)
{
dn->data[j+1]=dn->data[j];
}
dn->data[i]=k;
dn->datanum++;
if (dn->datanum>L)/*溢出需分裂*/
{
/*分裂为前后 两段 dn NewNode*/
DataNode *NewNode=new DataNode(dn->parent,dn,dn->next,dn->data);
if (dn->next)/*存在下一个数据节点*/
dn->next->pre=NewNode;
dn->next=NewNode;
if(!root)/*第一次分裂*/
{
root=new TreeNode(dn,NewNode->data[1],NewNode);/*后半段的第一个关键字放在插入其父节点*/
dn->parent=root;
NewNode->parent=root;
}
else
{
Insert(NewNode->data[1],NewNode,NewNode->parent);
}
}
}
}
void BPlusTree::DeleteBPlustree(int k)
{
/*仅有header 无 root*/
if(!root)
{
if (!header)
{
cout<<"B+tree is null !"<<endl;
return;
}
else
{
int i=1;
while (i<=header->datanum)
{
if (k==header->data[i])
{
for (int j=i;j<header->datanum;j++)
{
header->data[j]=header->data[j+1];
}
header->datanum--;
if(!header->datanum)
header=0;
return;
}
else
{
i++;
if(i==header->datanum)
{
cout<<"No this key :"<<k<<endl;
return ;
}
}
} }
}
/*找到关键字k在的元素节点 d（elete）node */
TreeNode *dnode=root;
int i=1;
while (dnode->keynum)/*不是元素节点则继续向下查找*/
{
i=1;
while(i<=dnode->keynum)
{
if (k>=dnode->key[i])
{
i++;
}
else
break;
}
/*左子树*/
dnode=dnode->ptr[i-1];
}
/* 找到相应的元素节点 dnode */
int index=i;
int minnum=ceil(L/2);/*元素节点最少关键字数目*/
DataNode *datanode=(DataNode*) dnode;
DataNode *la,*ra;/*该元素节点的左右节点*/
if (datanode->datanum>minnum)/*关键字足够多 ，移动覆盖即可*/
{
int i=1;
while (i<=datanode->datanum)
{
if (datanode->data[i]==k)
{
for (int j=i;j<datanode->datanum;j++)
{
datanode->data[j]=datanode->data[j+1];
}
datanode->data[j]=0;
datanode->datanum--;
return;
}
else
{
if (i==datanode->datanum)
{
cout<<"No this key"<<k<<endl;
return;
}
else
i++;
}
}
}
else/*元素不够多 从左右邻居节点借或者合并 由上面查找过程知*/
/*index 是该元素节点的索引*/
{
/*查找该关键字*/
int i=1;
while (i<=datanode->datanum)
{
/*找到并覆盖*/
if (datanode->data[i]==k)
{
for (int j=i;j<datanode->datanum;j++)
{
datanode->data[j]=datanode->data[j+1];
}
datanode->data[j]=0;
datanode->datanum--;
break;
}
else
{
if (i==datanode->datanum)
{
cout<<"No this key"<<k<<endl;
return;
}
else
i++;
}
}
/*删除后节点不完善*/ /*借*/
if (index-1)/*有左兄弟*/
{
la=(DataNode*)datanode->parent->ptr[index-2];
if (la->datanum>minnum)/*左兄弟的关键字足够多可以借*/
{
for (int j=datanode->datanum;j>=1;j--)
{
datanode->data[j+1]=datanode->data[j];
}
datanode->data[1]=la->data[la->datanum];/*最大关键字*/
datanode->parent->key[index-1]=la->data[la->datanum];
la->data[la->datanum]=0;
la->datanum--;
datanode->datanum++;
return;
}
}
if (index<=datanode->parent->keynum)/*有右兄弟*/
{ ra=(DataNode*)datanode->parent->ptr[index];
if (ra->datanum>minnum)/*右兄弟的关键字足够多可以借*/
{
/*加在datanode末尾*/
datanode->data[datanode->datanum+1]=ra->data[1];
datanode->datanum++;
datanode->parent->key[index]=ra->data[2];
/*右兄弟移动覆盖*/
for (int j=1;j<ra->datanum;j++)
{
ra->data[j]=ra->data[j+1];
}
ra->data[j]=0;
ra->datanum--;
return;
}
}
/*邻居节点的关键字不够多 合并*/
if (index-1)/*有左兄弟*/
{
/*关键字合并到左兄弟尾部 并且删除对应搜索节点的关键字*/
la=(DataNode*)datanode->parent->ptr[index-2];
for (int j=1;j<=datanode->datanum;j++)
{
la->data[la->datanum+1]=datanode->data[j];
}
la->parent->ptr[index-1]=0; la->next=datanode->next;
if (datanode->next)/*是尾节点*/
datanode->next->pre=la;
delete datanode;
DeleteBtree(la->parent->key[index-1]);
return;
}
if (index<=datanode->parent->keynum)/*有右兄弟*/
{
/*关键字合并到右兄弟头部 并且删除对应搜索节点的关键字*/
ra=(DataNode*)datanode->parent->ptr[index];
/*右兄弟关键字后移出位置以便合并*/
for (int j=ra->datanum;j>=1;j--)
{
ra->data[j+datanode->datanum]=ra->data[j];
}
/*填充到右兄弟节点头部*/
for (int l=1;l<=datanode->datanum;l++)
{
ra[l]=datanode[l];
}
ra->datanum+=datanode->datanum;
/*数据节点链操作 注意首尾的处理*/
ra->pre=datanode->pre;
if (datanode->pre)
{
datanode->pre->next=ra;
}
else
{
/*datanode 为 header*/
header=ra;
}
ra->parent->ptr[index-1]=0;
delete datanode;
DeleteBtree(ra->parent->key[index]);
return;
}
}
}