Match readings with latest same-city humidity

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.