Online assessment (NXT Engineering Test): the first of two coding problems.

You are given sources, a 2D array of strings. Each row is one source: a list of key-value entries such as P1:a. Return a 1D array of strings with one value per key, where

• a later source overrides the value an earlier source gave the same key, and
• the keys come out in the order they were first seen.

Example (as posted)

sources:
  P1:a  P3:b  P5:x
  P1:b  P2:q  P5:x

output: b b x q

The keys first appear in the order P1, P3, P5, P2. P1's value a from the first source is overridden by the second source's b, but P1 keeps its first position.

Notes from the report

• The poster calls the description convoluted but the problem itself simple string processing.
• Not reported, so confirm before coding:
  • the exact entry format: one "KEY:value" string per entry (as here), or key and value in separate cells, and whether spaces can sit around the colon (the post writes both P1: a and P3:b);
  • what happens if one source lists the same key twice.
• No input sizes were reported.