Binary Tree ASCII Printer

Binary Tree Printer.swift

import Foundation

// Ideally Node should be a struct.
// However Swift doesn't allow recursive value types at the moment.

class Node {
    var left, right: Node?
    var value: String
    
    init(value: String = "") {
        self.value = value
    }
    
    func toString() -> String {
        return buildTreeString(isTail: true)
    }
    
    private func buildTreeString(prefix: String = "", isTail: Bool) -> String {
        var result = ""
        
        if right != nil {
            let newPrefix = prefix + (isTail ? "│   " : "    ")
            result += right!.buildTreeString(prefix: newPrefix, isTail: false)
        }
        
        result += prefix + (isTail ? "└── " : "┌── ") + value + "\n"
        
        if left != nil {
            let newPrefix = prefix + (isTail ? "    " : "│   ")
            result += left!.buildTreeString(prefix: newPrefix, isTail: true)
        }
        
        return result
    }
    
}


// EXAMPLE

func buildExampleTree() -> Node {
    
    let root = Node(value: "2")
    let n11 = Node(value: "7")
    let n12 = Node(value: "5")
    let n21 = Node(value: "2")
    let n22 = Node(value: "6")
    let n23 = Node(value: "3")
    let n24 = Node(value: "6")
    let n31 = Node(value: "5")
    let n32 = Node(value: "8")
    let n33 = Node(value: "4")
    let n34 = Node(value: "5")
    let n35 = Node(value: "8")
    let n36 = Node(value: "4")
    let n37 = Node(value: "5")
    let n38 = Node(value: "8")
    
    root.left = n11
    root.right = n12
    
    n11.left = n21
    n11.right = n22
    n12.left = n23
    n12.right = n24
    
    n21.left = n31
    n21.right = n32
    n22.left = n33
    n22.right = n34
    n23.left = n35
    n23.right = n36
    n24.left = n37
    n24.right = n38
    
    return root
}

let tree = buildExampleTree()
println(tree.toString())

output.txt

│           ┌── 8
│       ┌── 6
│       │   └── 5
│   ┌── 5
│   │   │   ┌── 4
│   │   └── 3
│   │       └── 8
└── 2
    │       ┌── 5
    │   ┌── 6
    │   │   └── 4
    └── 7
        │   ┌── 8
        └── 2
            └── 5

This is excellent. Thanks 😄

Excellent indeed. Thank you!