Find the flipped card

JavaScript Advanced astronaut ages teen+ From CS Unplugged

The problem

A grid of cards is given as a list of rows, like ["BBW", "BWB", "WBB"]. Every row and every column should have an even number of B. Someone flipped one card. Write a function findFlippedCard(rows) that gives back [row, column] of that card, counting from 1. If every row and column is fine, give back null (None in Python).

You will practice: lists of text, nested loops, parity, error correction

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CC BY-SA 4.0

Adapted from a CS Unplugged programming challenge by the University of Canterbury Computer Science Education Research Group, licensed CC BY-SA 4.0.

Original challenge · License: CC BY-SA 4.0

Changes: Rewritten in our own words as a function with tests, hints and steps, in Python and JavaScript, by Open Cosmos. This version is also CC BY-SA 4.0.