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fix: SplayTree.remove is broken
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nghiahoang committed Jun 25, 2020
1 parent bcd9eb3 commit f4fb2fc
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Showing 4 changed files with 57 additions and 229 deletions.
33 changes: 7 additions & 26 deletions Splay Tree/SplayTree.playground/Contents.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -5,29 +5,10 @@
print("Hello, Swift 4!")
#endif

let splayTree = SplayTree(value: 1)
splayTree.insert(value: 2)
splayTree.insert(value: 10)
splayTree.insert(value: 6)

splayTree.remove(value: 10)
splayTree.remove(value: 6)

splayTree.insert(value: 55)
splayTree.insert(value: 559)
splayTree.remove(value: 2)
splayTree.remove(value: 1)
splayTree.remove(value: 55)
splayTree.remove(value: 559)

splayTree.insert(value: 1843000)
splayTree.insert(value: 1238)
splayTree.insert(value: -1)
splayTree.insert(value: 87)

splayTree.minimum()
splayTree.maximum()




var tree = SplayTree<Int>(value: 0)
tree.insert(value: 2)
tree.insert(value: 3)
tree.insert(value: 4)
tree.insert(value: 7)
_ = tree.search(value: 2)
tree.remove(value: 2)
122 changes: 22 additions & 100 deletions Splay Tree/SplayTree.playground/Sources/SplayTree.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -289,120 +289,42 @@ extension Node {
- Node Resulting from the deletion and the splaying of the removed node

*/
public func remove(value: T) -> Node<T>? {
let replacement: Node<T>?
fileprivate func remove(value: T) -> Node<T>? {
guard let target = search(value: value) else { return self }

if let v = self.value, v == value {
if let left = target.left, let right = target.right {
let largestOfLeftChild = left.maximum()
left.parent = nil
right.parent = nil

var parentToSplay: Node<T>?
if let left = left {
if let right = right {

replacement = removeNodeWithTwoChildren(left, right)

if let replacement = replacement,
let replacementParent = replacement.parent,
replacementParent.value != self.value {

parentToSplay = replacement.parent

} else if self.parent != nil {
parentToSplay = self.parent
} else {
parentToSplay = replacement
}

} else {
// This node only has a left child. The left child replaces the node.
replacement = left
if self.parent != nil {
parentToSplay = self.parent
} else {
parentToSplay = replacement
}
}
} else if let right = right {
// This node only has a right child. The right child replaces the node.
replacement = right
if self.parent != nil {
parentToSplay = self.parent
} else {
parentToSplay = replacement
}
} else {
// This node has no children. We just disconnect it from its parent.
replacement = nil
parentToSplay = parent
}

reconnectParentTo(node: replacement)
SplayOperation.splay(node: largestOfLeftChild)
largestOfLeftChild.right = right

// performs the splay operation
if let parentToSplay = parentToSplay {
SplayOperation.splay(node: parentToSplay)
}
return largestOfLeftChild

// The current node is no longer part of the tree, so clean it up.
parent = nil
left = nil
right = nil
} else if let left = target.left {
replace(node: target, with: left)
return left

return parentToSplay
} else if let right = target.right {
replace(node: target, with: right)
return right

} else if let v = self.value, value < v {
if left != nil {
return left!.remove(value: value)
} else {
let node = self
SplayOperation.splay(node: node)
return node

}
} else {
if right != nil {
return right?.remove(value: value)
} else {
let node = self
SplayOperation.splay(node: node)
return node

}
return nil
}
}

private func removeNodeWithTwoChildren(_ left: Node, _ right: Node) -> Node {
// This node has two children. It must be replaced by the smallest
// child that is larger than this node's value, which is the leftmost
// descendent of the right child.
let successor = right.minimum()
private func replace(node: Node<T>, with newNode: Node<T>?) {
guard let sourceParent = sourceNode.parent else { return }

// Connect our left child with the new node.
successor.left = left
left.parent = successor

// Connect our right child with the new node. If the right child does
// not have any left children of its own, then the in-order successor
// *is* the right child.
if right !== successor {
successor.right = right
right.parent = successor
if sourceNode.isLeftChild {
sourceParent.left = newNode
} else {
successor.right = nil
sourceParent.right = newNode
}

// And finally, connect the successor node to our parent.
return successor
}

private func reconnectParentTo(node: Node?) {
if let parent = parent {
if isLeftChild {
parent.left = node
} else {
parent.right = node
}
}
node?.parent = parent
newNode?.parent = sourceParent
}
}

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124 changes: 23 additions & 101 deletions Splay Tree/SplayTree.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ public enum SplayOperation {
- Returns
- Operation Case zigZag - zigZig - zig
*/
public static func operation<T: Comparable>(forNode node: Node<T>) -> SplayOperation {
public static func operation<T>(forNode node: Node<T>) -> SplayOperation {

if let parent = node.parent, let _ = parent.parent {
if (node.isLeftChild && parent.isRightChild) || (node.isRightChild && parent.isLeftChild) {
Expand Down Expand Up @@ -289,120 +289,42 @@ extension Node {
- Node Resulting from the deletion and the splaying of the removed node

*/
public func remove(value: T) -> Node<T>? {
let replacement: Node<T>?
fileprivate func remove(value: T) -> Node<T>? {
guard let target = search(value: value) else { return self }

if let v = self.value, v == value {
if let left = target.left, let right = target.right {
let largestOfLeftChild = left.maximum()
left.parent = nil
right.parent = nil

var parentToSplay: Node<T>?
if let left = left {
if let right = right {

replacement = removeNodeWithTwoChildren(left, right)

if let replacement = replacement,
let replacementParent = replacement.parent,
replacementParent.value != self.value {

parentToSplay = replacement.parent

} else if self.parent != nil {
parentToSplay = self.parent
} else {
parentToSplay = replacement
}

} else {
// This node only has a left child. The left child replaces the node.
replacement = left
if self.parent != nil {
parentToSplay = self.parent
} else {
parentToSplay = replacement
}
}
} else if let right = right {
// This node only has a right child. The right child replaces the node.
replacement = right
if self.parent != nil {
parentToSplay = self.parent
} else {
parentToSplay = replacement
}
} else {
// This node has no children. We just disconnect it from its parent.
replacement = nil
parentToSplay = parent
}
SplayOperation.splay(node: largestOfLeftChild)
largestOfLeftChild.right = right

reconnectParentTo(node: replacement)
return largestOfLeftChild

// performs the splay operation
if let parentToSplay = parentToSplay {
SplayOperation.splay(node: parentToSplay)
}
} else if let left = target.left {
replace(node: target, with: left)
return left

// The current node is no longer part of the tree, so clean it up.
parent = nil
left = nil
right = nil

return parentToSplay
} else if let right = target.right {
replace(node: target, with: right)
return right

} else if let v = self.value, value < v {
if left != nil {
return left!.remove(value: value)
} else {
let node = self
SplayOperation.splay(node: node)
return node

}
} else {
if right != nil {
return right?.remove(value: value)
} else {
let node = self
SplayOperation.splay(node: node)
return node

}
return nil
}
}

private func removeNodeWithTwoChildren(_ left: Node, _ right: Node) -> Node {
// This node has two children. It must be replaced by the smallest
// child that is larger than this node's value, which is the leftmost
// descendent of the right child.
let successor = right.minimum()
private func replace(node: Node<T>, with newNode: Node<T>?) {
guard let sourceParent = sourceNode.parent else { return }

// Connect our left child with the new node.
successor.left = left
left.parent = successor

// Connect our right child with the new node. If the right child does
// not have any left children of its own, then the in-order successor
// *is* the right child.
if right !== successor {
successor.right = right
right.parent = successor
if sourceNode.isLeftChild {
sourceParent.left = newNode
} else {
successor.right = nil
sourceParent.right = newNode
}

// And finally, connect the successor node to our parent.
return successor
}

private func reconnectParentTo(node: Node?) {
if let parent = parent {
if isLeftChild {
parent.left = node
} else {
parent.right = node
}
}
node?.parent = parent
newNode?.parent = sourceParent
}
}

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7 changes: 5 additions & 2 deletions Splay Tree/readme.md
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Original file line number Diff line number Diff line change
Expand Up @@ -102,8 +102,11 @@ To insert a value:

To delete a value:

- Delete it as in a binary search tree
- Splay the parent of the removed node to the root
- Perform search for the value, after performed search function if the tree contains the value, it'll be the root of the new tree.
- If the tree has only left child, change left child to the root of the tree, remove the old root node
- If the tree has only right child, change right child to the root of the tree, remove the old root node
- Else, the tree has both two children, set parent of two children to nil, so that they're two new trees (left-tree and right-tree).
- Splay the minimum node of right-tree (or minimum node of left-tree), then set left-tree as left child of new root of right-tree (or set right-tree as right child of new root of left-tree), return right-tree

### Search

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