Compute unique duration by merging intervals

Q: Compute unique duration by merging intervals

This is a Data Manipulation (SQL/Python) interview question from Nuro for Data Engineer roles. View the full question and solution on PracHub.

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Question

Problem

You have an autonomous-driving clip dataset where each row represents a time interval from a driving run.

Table: `clips`

column	type	description
`set_id`	INT	Session/clip set identifier (e.g., 1–6)
`run_id`	STRING	Driving run identifier, formatted like `YYYYMMDD_HHMMSS`
`start_time`	INT	Clip start time offset (e.g., seconds)
`end_time`	INT	Clip end time offset (e.g., seconds)
`set_number`	INT	Dataset/source identifier

Assume each interval is half-open: [start_time, end_time) so duration is end_time - start_time.

Intervals for the same run_id may:

overlap (partially or fully),
be duplicated/redundant,
have gaps (non-contiguous).

Task

Compute, for each run_id, the cumulative deduplicated time: the total duration covered by the union of all intervals for that run_id (i.e., after merging overlaps).

Example input

For run 20250101_122334:

set 1: [58, 70)
set 2: [57, 69)
set 3: [55, 72)
set 4: [56, 71)
set 5: [80, 100)

For run 20250102_101010:

set 6: [43, 62)

Expected output

Return a result with:

run_id
cumulative_unique_time (same unit as the time offsets)

Using the example above, results would be:

20250101_122334 → 39
20250102_101010 → 19

Requirements

Write a SQL solution to compute cumulative_unique_time per run_id .
Write a Python solution to compute the same metric (given a list/dataframe of intervals).