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Match readings with latest same-city humidity

Two SigmaData Scientist · Technical Screen
EasyData ScientistTechnical ScreenCoding & Algorithms

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This question evaluates the ability to align and join time-ordered sensor data by key, testing skills in time-series merging, per-key state management, and handling absent matches.

Problem

You are given two time-sorted lists of sensor readings:

  • Temperature records: (time, city, reading)
  • Humidity records: (time, city, reading)

Example:

Temperature

[(1, 'NYC', 12),
 (5, 'SFO', 20),
 (7, 'NYC', 23),
 (16, 'SFO', 10)]

Humidity

[(0, 'SFO', 12),
 (3, 'SFO', 2),
 (6, 'NYC', 2),
 (19, 'SFO', 9)]

Task

For each temperature record, match it with the most recent humidity record from the same city whose time <= temperature_time.

  • If there is no earlier humidity record for that city, return null (or None) for the humidity reading.

Output

Return a list aligned to the temperature records, where each element includes the temperature record and the matched humidity reading (or null).

Constraints

  • Both input lists are individually sorted by time ascending.
  • Cities may appear in any order within the global time ordering.