Parse Parent-Child Task Records and Render Them as a Connector Tree

You receive a list of task records and must rebuild the hierarchy of tasks and subtasks they describe, then print it as a text tree. The specification is long and the output format is strict, so reading carefully matters as much as the code. The exercise is split into parts; the first two are below.

There are two kinds of records:

• Root records contain the fields timestamp, task, task_id and task_name.
• Child records contain the fields timestamp, subtask, parent_id, task_id and task_name. The parent_id of a child is the task_id of its parent.

Clarifying Questions

• Is the result returned as one string or printed line by line, and is it compared character for character?
• How many records can there be, and how deep can the nesting go?

Part 1 — Parse the records into a parent-child map

Parse the records into a structure that maps every task to its child tasks and identifies the root tasks.

Clarifying Questions for this Part

• In what form do the records arrive: parsed objects, JSON lines or another text format?
• What do the task and subtask fields hold, and is a record's kind decided by them or by the presence of parent_id?
• Can a child have children of its own?
• What should happen to a record whose parent_id matches no task, or to two records that share a task_id?

What This Part Should Cover

• A map from each parent to its children, plus the list of roots, built independently of input order
• Handling of orphans, duplicate identifiers and cycles in the parent links
• Time and space complexity of the build

Part 2 — Render the tree with connectors

Print the hierarchy. A root node is printed without any leading connector. A child that is not the last among its siblings is printed after ├─, and the last child in a sibling group is printed after └─. For a root with two children, the output has this shape (the labels are placeholders):

Root task
├─ First child
└─ Last child

Clarifying Questions for this Part

• What text is printed for each node: the task name, the identifier, or both?
• In what order are siblings and roots printed: by timestamp, by input order or by identifier?
• For grandchildren and deeper nodes, what indentation goes in front of the connector?

What This Part Should Cover

• Deterministic sibling ordering and correct detection of the last child
• Correct prefixes at every depth, not only for the direct children of a root
• A traversal that is safe for deep trees, and its cost