Render an Organization Chart and Find Skip-Level Pairs

Build an organization tree from manager/direct-report rows. Support rendering the tree with indentation and listing all skip-level pairs, where the second employee is exactly two edges below the first.

Implement org_chart(relations: string[][], mode: int) -> string[]:

• A row [manager, child1, child2, ...] lists that manager's direct reports in display order.
• mode == 0: return the rendered lines in preorder. Prefix each employee with four dots per depth level; the root has no prefix.
• mode == 1: return skip-level pairs encoded as manager,employee, with one comma and no spaces. Visit managers in tree preorder; for each manager, visit its children and then each child's children in the stored order.

Constraints & Assumptions

• Each employee name is a nonempty ASCII string of letters, digits, or underscores.
• Each manager appears as the first item of at most one row, and no direct-report list contains a duplicate.
• The rows describe one valid rooted tree with at most 2,000 employees: no cycles, one parent per non-root employee, and exactly one root. The root is not separately supplied.
• A one-element row can represent an employee with no reports. An empty relation list represents an empty chart and returns an empty list in either mode.
• Employees that appear only as children are leaves. Preserve input child order; do not alphabetize it.
• The mode interface and pair serialization are explicit practice encodings of the reported class methods. Skip-level means exactly two levels, not all descendants beyond one level.

Examples

relations = [["A","B","C"],["B","E"],["C","D"]]
mode = 0
result = ["A","....B","........E","....C","........D"]

relations = [["A","B","C"],["B","E"],["C","D"]]
mode = 1
result = ["A,E","A,D"]

Explain the time and space costs of building the tree, rendering it, and listing skip-level pairs, including the size of the returned strings. Describe tests for a single root, a chain, and a branching tree.