Commit 791cc66

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Merge pull request #868 from dcherednikov/red-black-tree-enhancement

Add getPredecessor() and getKey() methods to RBTreeNode.

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Red-Black Tree
- README.markdown
- RedBlackTree.playground/Sources
  - RedBlackTree.swift

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Original file line number	Diff line number	Diff line change
`@@ -29,6 +29,7 @@ From [CLRS]`
`29`	`29`	`## Methods`
`30`	`30`
`31`	`31`	`Nodes:`
	`32`	+* `nodeX.getPredecessor()` Returns the inorder predecessor of nodeX
`32`	`33`	* `nodeX.getSuccessor()` Returns the inorder successor of nodeX
`33`	`34`	* `nodeX.minimum()` Returns the node with the minimum key of the subtree of nodeX
`34`	`35`	* `nodeX.maximum()` Returns the node with the maximum key of the subtree of nodeX

Lines changed: 26 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -60,6 +60,10 @@ public class RBTreeNode<T: Comparable>: Equatable {`
`60`	`60`	`self.init(key: nil, leftChild: nil, rightChild: nil, parent: nil)`
`61`	`61`	`self.color = .black`
`62`	`62`	`}`
	`63`	`+`
	`64`	`+ public func getKey() -> T? {`
	`65`	`+ return key`
	`66`	`+ }`
`63`	`67`
`64`	`68`	`var isRoot: Bool {`
`65`	`69`	`return parent == nil`
`@@ -120,9 +124,30 @@ extension RBTreeNode {`
`120`	`124`	`}`
`121`	`125`	`}`
`122`	`126`
`123`		`-// MARK: - Finding a nodes successor`
	`127`	`+// MARK: - Finding a nodes successor and predecessor`
`124`	`128`
`125`	`129`	`extension RBTreeNode {`
	`130`	`+ /*`
	`131`	`+ * Returns the inorder predecessor node of a node`
	`132`	`+ * The predecessor is a node with the next smaller key value of the current node`
	`133`	`+ */`
	`134`	`+ public func getPredecessor() -> RBNode? {`
	`135`	`+ // if node has left child: predecessor is min of this left tree`
	`136`	`+ if let leftChild = leftChild, !leftChild.isNullLeaf {`
	`137`	`+ return leftChild.maximum()`
	`138`	`+ }`
	`139`	`+ // else go upward while node is left child`
	`140`	`+ var currentNode = self`
	`141`	`+ var parent = currentNode.parent`
	`142`	`+ while currentNode.isLeftChild {`
	`143`	`+ if let parent = parent {`
	`144`	`+ currentNode = parent`
	`145`	`+ }`
	`146`	`+ parent = currentNode.parent`
	`147`	`+ }`
	`148`	`+ return parent`
	`149`	`+ }`
	`150`	`+`
`126`	`151`	`/*`
`127`	`152`	`* Returns the inorder successor node of a node`
`128`	`153`	`* The successor is a node with the next larger key value of the current node`

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