The Last Known Good

A medium Python interview practice problem on DataDriven. Write and execute real python code with instant grading.

Domain

Python

Difficulty

medium

Seniority

L4

Problem

You're aligning two parallel columns from a sensor export, `left` and `right`, that can stop reporting at different points. Pair them position by position into `[left_i, right_i]` rows for as many positions as the longer column has, and when one column runs out partway, carry its last reported value forward to fill its side of the remaining rows. If a column is empty from the start there's no value to carry, so leave that side as `None`.

Summary

When a column goes quiet, its last reading keeps standing.

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