def delete(self, anItem):
''' Answer None if a matching item is not found. If found,
answer the entire item.
'''
searchResult = self.searchTree(anItem)
n = self.degree
if searchResult['found']: #the item is in the tree; delete it
aNode = self.readFrom(
searchResult['fileIndex']) #get the node that contains anItem
nodeIndex = searchResult['nodeIndex']
done = False
if not aNode.isLeaf(
): #if anItem is in a leaf node, find the inorder successor
(ioSuc, iosNode) = self.inorderSuccessor(aNode, nodeIndex)
searchResult = self.searchTree(
ioSuc
) #search the tree in order to get the stack of nodes on the search path
aNode.getItems(
)[nodeIndex] = ioSuc #replace anItem with the inorder successor
iosNode.removeItem(
0) #remove the inorder successor from its original node
self.writeAt(aNode.getIndex(),
aNode) #write the revised aNode to the file
aNode = iosNode #reset what aNode refers to
anItem = ioSuc
else: #if anItem was already in a leaf node
aNode.removeItem(nodeIndex) #remove anItem from the leaf node
while not done and aNode.getNumberOfKeys() < n and aNode.getIndex(
) != self.rootIndex: #while aNode has less than n keys and is not the root
parentNode = self.stackOfNodes.pop() #get the parent node
(parentIndex,
siblingNode, sibSide) = self.findParentAndSibling(
anItem, parentNode) #get the parent index and the sibling
totNumKeys = siblingNode.getNumberOfKeys(
) + aNode.getNumberOfKeys(
) + 1 #find the total number of keys, including the parent item
tempNode = BTreeNode(2 * n) #create a temporary BTreeNode
if sibSide == "right": #if using the right sibling, copy aNode, then parent, then sibling
tempNode.copyItemsAndChildren(aNode, 0,
aNode.getNumberOfKeys() - 1,
0)
tempNode.getItems()[aNode.getNumberOfKeys(
)] = parentNode.getItems()[parentIndex]
tempNode.copyItemsAndChildren(
siblingNode, 0,
siblingNode.getNumberOfKeys() - 1,
aNode.getNumberOfKeys() + 1)
else: #if using the left sibling, copy the sibling, then parent, then aNode
tempNode.copyItemsAndChildren(
siblingNode, 0,
siblingNode.getNumberOfKeys() - 1, 0)
tempNode.getItems()[siblingNode.getNumberOfKeys(
)] = parentNode.getItems()[parentIndex]
tempNode.copyItemsAndChildren(
aNode, 0,
aNode.getNumberOfKeys() - 1,
siblingNode.getNumberOfKeys() + 1)
aNode.clear() #clear the items and children from the two nodes
siblingNode.clear()
if totNumKeys > 2 * n: #case 2a: redistribute
sepKey = (totNumKeys +
1) // 2 #find the new separating key
aNode.copyItemsAndChildren(
tempNode, 0, sepKey - 2, 0
) #put the items of the temp node back to where they belong, redistributed
parentNode.getItems()[parentIndex] = tempNode.getItems()[
sepKey - 1]
siblingNode.copyItemsAndChildren(tempNode, sepKey,
totNumKeys - 1, 0)
aNode.setNumberOfKeys(sepKey - 1)
siblingNode.setNumberOfKeys(totNumKeys - sepKey)
else: #case 2b: merge
parentNode.removeItem(
parentIndex
) #remove the parent item from the parent node
if sibSide == "right": #remove the child representing the right sibling
parentNode.removeChild(parentIndex + 1)
if parentNode.getNumberOfKeys(
) == 0: #if the parent is now empty after the merge, make aNode the root of the tree
done = True
self.rootNode = aNode
self.rootIndex = aNode.getIndex()
aNode.copyItemsAndChildren(
tempNode, 0, totNumKeys - 1,
0) #merge all the items into aNode
aNode.setNumberOfKeys(totNumKeys)
else: #remove the child representing the right sibling (aNode)
parentNode.removeChild(parentIndex + 1)
if parentNode.getNumberOfKeys(
) == 0: #if the parent is now empty after the merge, make sibNode the root of the tree
done = True
self.rootNode = siblingNode
self.rootIndex = siblingNode.getIndex()
siblingNode.copyItemsAndChildren(
tempNode, 0, totNumKeys - 1,
0) #merge all the items into the sibling node
siblingNode.setNumberOfKeys(totNumKeys)
self.writeAt(aNode.getIndex(),
aNode) #write the updates to the file
self.writeAt(siblingNode.getIndex(), siblingNode)
self.writeAt(parentNode.getIndex(), parentNode)
aNode = parentNode #move up the tree and check if it's ok
else: #the item is not in the tree; return None
return None
def delete(self, anItem):
''' Answer None if a matching item is not found. If found,
answer the entire item.
'''
searchResult = self.searchTree(anItem)
n = self.degree
if searchResult['found']: #the item is in the tree; delete it
aNode = self.readFrom(searchResult['fileIndex']) #get the node that contains anItem
nodeIndex = searchResult['nodeIndex']
done = False
if not aNode.isLeaf(): #if anItem is in a leaf node, find the inorder successor
(ioSuc, iosNode) = self.inorderSuccessor(aNode, nodeIndex)
searchResult = self.searchTree(ioSuc) #search the tree in order to get the stack of nodes on the search path
aNode.getItems()[nodeIndex] = ioSuc #replace anItem with the inorder successor
iosNode.removeItem(0) #remove the inorder successor from its original node
self.writeAt(aNode.getIndex(), aNode) #write the revised aNode to the file
aNode = iosNode #reset what aNode refers to
anItem = ioSuc
else: #if anItem was already in a leaf node
aNode.removeItem(nodeIndex) #remove anItem from the leaf node
while not done and aNode.getNumberOfKeys() < n and aNode.getIndex() != self.rootIndex: #while aNode has less than n keys and is not the root
parentNode = self.stackOfNodes.pop() #get the parent node
(parentIndex, siblingNode, sibSide) = self.findParentAndSibling(anItem, parentNode) #get the parent index and the sibling
totNumKeys = siblingNode.getNumberOfKeys() + aNode.getNumberOfKeys() + 1 #find the total number of keys, including the parent item
tempNode = BTreeNode(2*n) #create a temporary BTreeNode
if sibSide == "right": #if using the right sibling, copy aNode, then parent, then sibling
tempNode.copyItemsAndChildren(aNode, 0, aNode.getNumberOfKeys()-1, 0)
tempNode.getItems()[aNode.getNumberOfKeys()] = parentNode.getItems()[parentIndex]
tempNode.copyItemsAndChildren(siblingNode, 0, siblingNode.getNumberOfKeys()-1, aNode.getNumberOfKeys()+1)
else: #if using the left sibling, copy the sibling, then parent, then aNode
tempNode.copyItemsAndChildren(siblingNode, 0, siblingNode.getNumberOfKeys()-1, 0)
tempNode.getItems()[siblingNode.getNumberOfKeys()] = parentNode.getItems()[parentIndex]
tempNode.copyItemsAndChildren(aNode, 0, aNode.getNumberOfKeys()-1, siblingNode.getNumberOfKeys()+1)
aNode.clear() #clear the items and children from the two nodes
siblingNode.clear()
if totNumKeys > 2*n: #case 2a: redistribute
sepKey = (totNumKeys + 1)//2 #find the new separating key
aNode.copyItemsAndChildren(tempNode, 0, sepKey-2, 0) #put the items of the temp node back to where they belong, redistributed
parentNode.getItems()[parentIndex] = tempNode.getItems()[sepKey-1]
siblingNode.copyItemsAndChildren(tempNode, sepKey, totNumKeys-1, 0)
aNode.setNumberOfKeys(sepKey-1)
siblingNode.setNumberOfKeys(totNumKeys-sepKey)
else: #case 2b: merge
parentNode.removeItem(parentIndex) #remove the parent item from the parent node
if sibSide == "right": #remove the child representing the right sibling
parentNode.removeChild(parentIndex+1)
if parentNode.getNumberOfKeys() == 0: #if the parent is now empty after the merge, make aNode the root of the tree
done = True
self.rootNode = aNode
self.rootIndex = aNode.getIndex()
aNode.copyItemsAndChildren(tempNode, 0, totNumKeys-1, 0) #merge all the items into aNode
aNode.setNumberOfKeys(totNumKeys)
else: #remove the child representing the right sibling (aNode)
parentNode.removeChild(parentIndex+1)
if parentNode.getNumberOfKeys() == 0: #if the parent is now empty after the merge, make sibNode the root of the tree
done = True
self.rootNode = siblingNode
self.rootIndex = siblingNode.getIndex()
siblingNode.copyItemsAndChildren(tempNode, 0, totNumKeys-1, 0) #merge all the items into the sibling node
siblingNode.setNumberOfKeys(totNumKeys)
self.writeAt(aNode.getIndex(), aNode) #write the updates to the file
self.writeAt(siblingNode.getIndex(), siblingNode)
self.writeAt(parentNode.getIndex(), parentNode)
aNode = parentNode #move up the tree and check if it's ok
else: #the item is not in the tree; return None
return None
