[SS-003] Removing element from RBTree

[J0onYEong]

New features

• removing element from RBTree
• restructure logic editted

restructure logic editted

When restructuring occurred, the original children of the node becoming the new parent were being discarded. I have added logic to properly reassign the original children into the restructured tree.

a method that appends node to certaion node is implemented

func append(_ value: Element) throws {
    
    guard let rootNode else {
        // Root node is empty
        createRoot(value)
        return
    }
    
    // new node is always red
    let newNode: RBTreeNode = .init(value: value, color: .red)
    
    // append new node
    try append(newNode, to: rootNode)
}
private func append(_ node: Node, to: Node) throws {
    
    var currentParentNode: RBTreeNode! = to
    
    while(true) {
        
        if currentParentNode.isEmptyNode {
            // CurrentNode is empty leaf node
            currentParentNode.parent?.setToChild(node)
            break
        }
        
        if currentParentNode > node {
            // go left
            currentParentNode = currentParentNode.leftChild
        } else if currentParentNode < node {
            // go right
            currentParentNode = currentParentNode.rightChild
        } else {
            throw RBTreeError.duplicatedElement
        }
    }
    
    // start checking double red
    resolveDoubleRed(node)
}

below code is added to end of the restructuring method

[originalLeftNode, originalRightNode]
    .compactMap { $0 }
    .forEach { relocatingNode in
        // this insertion not related to duplication
        try! append(relocatingNode, to: middleNode)
    }