Flatten Nested Comments

Flatten Nested Comments

In a social networking app, comments can be nested under parent comments, forming a tree-like structure. You are given a root list of Comment objects. Each comment may contain a list of replies, which are also Comment objects.

Your task is to implement a function that flattens this nested structure into a single list of objects, while preserving the visual hierarchy by adding a depth property to each comment.

Data Structure

class Comment {
    let id: String
    let text: String
    let replies: [Comment]
    var depth: Int = 0 // To be populated during flattening

    init(id: String, text: String, replies: [Comment] = []) {
        self.id = id
        self.text = text
        self.replies = replies
    }
}

Function Signature

func flattenComments(rootComments: [Comment]) -> [Comment]

Examples

Input: A structure like: C1 -> [C2 -> [C3], C4]

Output: [C1(depth: 0), C2(depth: 1), C3(depth: 2), C4(depth: 1)]

Constraints

• The nesting depth is unknown but will not cause a stack overflow in a typical UI scenario.
• You should return a new list of comment objects with their depth property correctly assigned.
• The order of comments must be consistent with a pre-order traversal (Parent before Children, Children in order of appearance).