Efficient sort array by ParentId swift - swift

Question

Given an array of dictionaries some of which have ParentId I need to sort them in ancestry order.
I have a working algorithm, but I am not sure it is actually efficient.
How can this be improved?
Sample data:
var dicts = [["ParentId": "eee82", "Id":"a0dq1"],
["ParentId": "pqrst", "Id":"eee82"],
["ParentId": "aaa1", "Id":"pqrst"]]
Sample output
["pqrst", "eee82", "a0dq1"]
I ran below in playground
import Foundation
// GIVEN this source...
var dicts = [["ParentId": "eee82", "Id":"a0dq1"],
["ParentId": "pqrst", "Id":"eee82"],
["ParentId": "aaa1", "Id":"pqrst"]]
func findParents(source: [[String:String]], this: [String:String]) -> [[String:String]] {
var results = [[String:String]]()
if let parentId = this["ParentId"],
let parent = source.first(where: { $0["Id"] == parentId }) {
results.append(parent)
results.append(contentsOf: findParents(source: source, this: parent))
}
return results
}
var this = dicts.first!
var accounts = (findParents(source: dicts, this: this) + [this])
var sorted = [[String:String]]()
var hasParentMap = [String: Bool]()
for account in accounts {
let parentId = account["ParentId"]
let hasParent = accounts.first(where: { $0["Id"] == parentId }) != nil
hasParentMap[account["Id"]!] = !(parentId == nil || !hasParent)
}
while sorted.count != accounts.count {
for account in accounts {
if sorted.first(where: { $0["Id"] == account["Id"] }) != nil {
continue
}
if hasParentMap[account["Id"]!] == false {
sorted.insert(account, at: 0)
continue
} else if let parentId = account["ParentId"] {
let parentIndex = sorted.firstIndex(where: { $0["Id"] == parentId })
if parentIndex == nil {
continue
}
sorted.insert(account, at: parentIndex! + 1)
}
}
}
dump (accounts.map({ $0["Id"]! })) // ["eee82", "pqrst", "a0dq1"]
// ...we want to get this output
dump (sorted.map({ $0["Id"]! })) // ["pqrst", "eee82", "a0dq1"]
Update removed the numerical ids to avoid confusion
Here's the visual illustration of what I am trying to achieve

Answer 1

To make things easier I created a Person type:
struct Person: Comparable, CustomStringConvertible {
let id: String
let parentID: String
var description: String {
return "[\(id), \(parentID)]"
}
static func < (lhs: Self, rhs: Self) -> Bool {
return lhs.id < rhs.id
}
init?(dict: [String: String]) {
guard let id = dict["Id"] else { return nil }
guard let parentID = dict["ParentId"] else { return nil }
self.id = id
self.parentID = parentID
}
func toDictionary() -> [String: String] {
return ["Id": id, "ParentId": parentID]
}
}
Here is our data:
var dicts = [
["ParentId": "2", "Id":"3"],
["ParentId": "1", "Id":"2"],
["ParentId": "42", "Id":"1"],
["ParentId": "100", "Id":"88"],
["ParentId": "88", "Id":"77"],
["ParentId": "77", "Id":"66"],
["ParentId": "77", "Id":"55"],
]
Here are our people converted to structs:
var people = dicts.compactMap { Person(dict: $0) }
Here are a few methods to operate on our array of people:
extension Array where Element == Person {
func tree(root: Person) -> [Person] {
[root] + children(of: root)
.flatMap { tree(root: $0) }
}
func topLevelParents() -> [Person] {
return filter { parent(of: $0) == nil }
}
func children(of parent: Person) -> [Person] {
return filter { $0.parentID == parent.id }.sorted()
}
func parent(of child: Person) -> Person? {
return first { child.parentID == $0.id }
}
}
Get all people who don't have parents:
let topLevelParents = people.topLevelParents().sorted()
print("topLevelParents: \(topLevelParents)")
Construct the tree of descendants for each parent and flatten into an array:
let results = topLevelParents.flatMap({ people.tree(root: $0) })
print("results: \(results)")
Convert back to a dictionary:
let dictionaryResults = results.map { $0.toDictionary() }
print("dictionaryResults: \(dictionaryResults)")