从B树删除
[英]Deletion from B tree
问题描述
I have question in my homework its about b-tree deletion with minimum branching factor t=2. 
我在作业中有一个疑问，它涉及以最小分支因子t = 2删除b树。
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [W]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R Y
/ | \ / \ / \ / \ / \
A C F I K M O Q ST X Z
Now after deleting Y from the above tree i get the final tree.. 现在从上述树中删除Y后，我得到了最后一棵树。
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [W]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R X
/ | \ / \ / \ / \ / \
A C F I K M O Q S T Z
Will this be the final tree after Deleting Y... i am not sure thats why posting here to be corrected..thankss 这将是删除Y之后的最后一棵树吗...我不确定这就是为什么要在此处进行更正..谢谢
3 个解决方案
解决方案1
0 已采纳 2013-10-19 16:54:52
I don't think it's correct, T cannot be in the right sub-tree of W since T comes before W. 我认为这是不对的，因为T在W之前，所以T不能在W的正确子树中。
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [T]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R X
/ | \ / \ / \ / \ / \
A C F I K M O Q S W Z
Here are the steps: 步骤如下：
Remove Y: 移除Y：
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [W]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R null
/ | \ / \ / \ / \ / \
A C F I K M O Q ST X Z
Replace with smallest from right sub-tree (Z), rebalance at Z's old location 用右侧子树（Z）中最小的替换，在Z的旧位置重新平衡
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [W]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R Z
/ | \ / \ / \ / \ /
A C F I K M O Q ST X
Cannot borrow from sibling (X), merge children at Z: 无法从同级（X）借用，在Z处合并子代：
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [W]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R [X,Z]
/ | \ / \ / \ / \
A C F I K M O Q ST
Cannot borrow from sibling (R), merge children at W: 无法从同级（R）借用，在W处合并子代：
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [Q,R,S,T,W,X,Z]
/ | \
/ | \
/ | \
BD J N
/ | \ / \ / \
A C F I K M O
Merged node (previously W) is now too large, split evenly: 合并的节点（以前为W）现在太大，平均分配：
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [T]
/ | \ / \
/ | \ [Q,R,S] [W,X,Z]
/ | \
BD J N
/ | \ / \ / \
A C F I K M O
Left node of T is now too large, split evenly: T的左节点现在太大了，请平均分配：
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [T]
/ | \ / \
/ | \ / [W,X,Z]
/ | \ /
BD J N R
/ | \ / \ / \ / \
A C F I K M O Q S
Right node of T is also too large, split evenly: T的右节点也太大，平均分配：
[P]
/ \
/ \
/ \
/ \
/ \
[G][L] [T]
/ | \ / \
/ | \ / \
/ | \ / \
BD J N R X
/ | \ / \ / \ / \ / \
A C F I K M O Q S W Z
解决方案2
0 2013-10-24 18:24:32
it is so good question. 这是一个很好的问题。 L goes to the root, P goes to it's right child and sit near WN and it's children becomes left child of P for delete Y, W must go middle down of R and YY goes down between X and Z now you can delete Y ... L移到根，P移到它的右子并坐在WN附近，它的子成为P的左子，以删除Y，W必须移到R的中间，而YY在X和Z之间向下移，现在您可以删除Y .. 。
[ L ]
/ \
!!!!!! !!!!!! / \\ / \\ / \\ / \\ / / / \\ / \\ / \\
[G] [P] / \\ / \\ / \\ / \\ / \\ / \\ [BD] [J] NRW [G] [P] / \\ / \\ / \\ / \\ / \\ / \\ [BD] [J] NRW
/ | / | \\ / \\ / \\ / | \\ / \\ / \\ / | | \\ \\
ACFIKMOQ ST XZ --->Y ACFIKMOQ ST XZ ---> Y
解决方案3
0 2013-10-24 18:27:46
it is so good question. 这是一个很好的问题。 L goes to the root, P goes to it's right child and sit near WN and it's children becomes left child of P for delete Y, W must go middle down of R and YY goes down between X and Z now you can delete Y ... L移到根，P移到它的右子并坐在WN附近，它的子成为P的左子，以删除Y，W必须移到R的中间，而YY在X和Z之间向下移，现在您可以删除Y .. 。
[ L ]
/ \
/ \
/ \
/ \
/ \
[G] [P]
/ \ / \
/ \ / \
/ \ / \
[B D] [J] N R W
/ | \ / \ / \ / | \
A C F I K M O Q ST X Z --->Y
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