EasyCoding

Check if Grid Satisfies Conditions

Asked at

Goldman Sachs

1Give yourself 5 minutes

2Answer out loud, not in your head

3Then compare with the answer below

Stuck? Show a way to structure it+

01Restate the vertical and horizontal conditions.
02Visit every cell once.
03Compare with the cell below when present.
04Compare with the cell to the right when present.
05Return on the first violation.

Reference answer

For the stated grid predicate, scan each coordinate (r, c) and only compare neighbours that exist. The usual conditions are that vertically adjacent cells are equal while horizontally adjacent cells are different: if r + 1 is in bounds, reject when grid[r][c] differs from grid[r+1][c]; if c + 1 is in bounds, reject when grid[r][c] equals grid[r][c+1]. Checking only down and right covers every adjacent pair once and avoids duplicate work. Explain the boundary guards before coding; a one-row or one-column grid is a useful sanity check. Do not assume the grid is square. With R rows and C columns, the scan is O(RC) time and O(1) auxiliary space.

Then expect these follow-ups

How would you report the first failing coordinate?
Tests: follow-up reasoning
What property holds for a one-column grid?
Tests: follow-up reasoning

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