Lowest common ancestor in swift.

LCA.swift

class Tree {
    let value: Int
    var left: Tree?
    var right: Tree?
    
    init(_ v: Int) {
        self.value = v
    }
}

let root = Tree(1)
let firstRight = Tree(2)
let firstLeft = Tree(3)
let firstLeftLeft = Tree(4)
let firstLeftRight = Tree(6)
let firstRightRight = Tree(7)
let firstRightLeft = Tree(5)

root.left = firstLeft
root.right = firstRight

firstLeft.left = firstLeftLeft
firstLeft.right = firstLeftRight

firstRight.right = firstRightRight
firstRight.left = firstRightLeft


func LCA(_ root: Tree?, _ a: Tree?, _ b: Tree?) -> Tree? {
    if root == nil  { return nil }
    if a?.value == root?.value || b?.value == root?.value { return root }
    
    let left = LCA(root?.left, a, b)
    let right = LCA(root?.right, a, b)
    
    if left != nil && right != nil  { return root }
    
    if left != nil { return left }
    if right != nil { return right }
    
    return nil
}

if let answ = LCA(root, firstRightLeft, firstLeftRight) {
    print(answ.value) // result "1\n"
}