class Tree {

var value: Int

var children: [Tree]

init(value: Int, children: [Tree] = []) {

self.value = value

self.children = children

}

}

class CourseTreeHeight {

func process(parents: [Int]) -> Int {

var dict: [Int: [Int]] = [:] // Parent value: Children values

for (i, parent) in parents.enumerated() { // i - child value, parent - parent value

dict[parent, default: []] += [i]

}

guard let parentValue = dict.removeValue(forKey: -1)?.first else { fatalError("No root in the tree") }

let root = Tree(value: parentValue)

fillTree(with: root, dict: dict)

return treeHeight(node: root)

}

func fillTree(with root: Tree, dict: [Int: [Int]]) {

guard let childValues = dict[root.value] else { return }

root.children = childValues.map { Tree(value: $0) }

for c in root.children {

fillTree(with: c, dict: dict)

}

}

func treeHeight(node: Tree?) -> Int {

var height = 1

for c in node?.children ?? [] {

height = max(height, treeHeight(node: c) + 1)

}

return height

}

func tests() {

print(process(parents: [4, -1, 4, 1, 1])) // 3

print(process(parents: [-1, 0, 4, 0, 3])) // 4

print(process(parents: [9, 7, 5, 5, 2, 9, 9, 9, 2, -1])) // 4

}

}