write a b tree in swift

To write a B-tree in Swift, you can follow these steps:

  1. Define a class or struct for the B-tree node. Each node will have an array of keys, an array of child nodes, and a boolean flag indicating if it is a leaf node.
main.swift
class BTreeNode<Key: Comparable> {
    var keys: [Key] = []
    var childNodes: [BTreeNode] = []
    var isLeaf: Bool = true
}

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  1. Implement the insertion method for the B-tree. Start by searching for the correct node to insert the key. If the node is full, split the node into two and promote the middle key to the parent.
main.swift
func insert(_ key: Key) {
    if root == nil {
        root = BTreeNode()
        root?.keys.append(key)
    } else {
        let newChild = root?.insert(key)
        if newChild != nil {
            let oldRoot = root
            root = BTreeNode()
            root?.keys.append(newChild!.keys[0])
            root?.childNodes = [oldRoot, newChild!]
            root?.isLeaf = false
        }
    }
}

extension BTreeNode {
    func insert(_ key: Key) -> BTreeNode? {
        var index = 0
        while index < keys.count && keys[index] < key {
            index += 1
        }
        if index < keys.count && keys[index] == key {
            return nil
        }
        if isLeaf {
            keys.insert(key, at: index)
            return self
        } else {
            let childNode = childNodes[index]
            let newChild = childNode.insert(key)
            if newChild != nil {
                keys.insert(newChild!.keys[0], at: index)
                childNodes.insert(newChild!, at: index + 1)
                if keys.count > maxKeys {
                    return split()
                }
            }
            return nil
        }
    }
    
    func split() -> BTreeNode {
        let middleIndex = keys.count / 2
        let middleKey = keys[middleIndex]
        
        let rightNode = BTreeNode()
        rightNode.keys = Array(keys[(middleIndex + 1)...])
        rightNode.childNodes = Array(childNodes[(middleIndex + 1)...])
        
        keys.removeSubrange(middleIndex...)
        childNodes.removeSubrange((middleIndex + 1)...)
        
        rightNode.isLeaf = isLeaf
        isLeaf = false

        return rightNode
    }
}

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  1. Create an instance of the B-tree and call the insert method to insert keys into the tree.
main.swift
let bTree = BTree<Int>()
bTree.insert(5)
bTree.insert(10)
bTree.insert(3)

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This is a basic implementation of a B-tree in Swift. You can further enhance it by adding methods for deletion, searching, and balancing the tree. Remember to adjust the maxKeys value according to the B-tree variant you want to implement.

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related categories

swift
data-structures
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