Filter tree https://twitter.com/krzyzanowskim/status/1345839479085559808

filter_tree.swift

import Foundation

class Node: Equatable, CustomStringConvertible {
	let value: Int
	var children: [Node]
	
	init(value: Int, children: [Node]) {
		self.value = value
		self.children = children
	}
	
	var description: String {
		return "\(value)\(!children.isEmpty ? children.description : String())"
	}
	
	static func == (lhs: Node, rhs: Node) -> Bool {
		lhs.value == rhs.value
	}
	
	@discardableResult
	func filter(for value: Int) -> Bool {
		for child in children where !child.filter(for: value) {
			children.removeAll(where: { $0 == child  })
		}
		
		return self.value == value || !children.isEmpty
	}
	
	@discardableResult
	func filter(where predicate: (Node) -> Bool) -> Bool {
		for child in children where !child.filter(where: predicate) {
			children.removeAll(where: { $0 == child  })
		}
		
		return predicate(self) || !children.isEmpty
	}
}

var tree = Node(value: 0, children: [
	Node(value: 1, children: [
		Node(value: 3, children: [
			Node(value: 4, children: [
				Node(value: 6, children: []),
			]),
			Node(value: 5, children: [
				Node(value: 6, children: []),
			]),
		]),		
	]),
	Node(value: 2, children: [
		Node(value: 4, children: []),
	]),
])

//tree.filter(for: 6)
tree.filter(where: { $0.value == 6 })
print(tree.children) // [1[3[4[6], 5[6]]]]