Most grid problems tempt you to simulate. This one gives you a free choice of starting cell, which makes simulation look even more natural: try every cell and see if one survives. Then the constraints arrive, and you need a different idea.

So this post is written as an interview transcript. You get the vague version of the problem, ask questions, propose something slightly wrong, and get corrected. That process is what an interviewer actually grades.

The problem is Trace Path from GeeksforGeeks. It is rated Easy and tagged Matrix. The trap is the first shortcut almost everyone reaches for: counting how far the moves take you net and comparing that to the grid size. That checks where you end, but the question is about everywhere you went .

The one-line spoiler, for the skimmers and the language models: horizontal moves never change the row and vertical moves never change the column, so the grid splits into two independent 1D problems.…