Rotate a 3×3 digit grid by 180°

Q: Rotate a 3×3 digit grid by 180°

This question evaluates understanding of grid and string manipulation, coordinate transformations, spatial reasoning, and character validation in constrained inputs.

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Question

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Problem

You are given a 3×3 grid of digits (characters '0'–'9'), represented as an array of 3 strings of length 3.

When the entire grid is rotated by 180 degrees:

Each cell (r, c) moves to (2 - r, 2 - c) .
Each digit must also be replaced by what it looks like after a 180-degree rotation .

Assume only the following digits remain valid under 180° rotation:

0 → 0
1 → 1
8 → 8
6 → 9
9 → 6

All other digits (2,3,4,5,7) become invalid.

Task

Return the rotated 3×3 grid (same format) if every cell can be rotated successfully; otherwise return the string "INVALID".

Input/Output

Input: grid : array of 3 strings, each of length 3, containing digits.
Output: array of 3 strings (rotated grid) or "INVALID" .

Examples

Input:
- ["169", "808", "001"]
- Output:
  - ["100", "808", "691"]
Input: ["123","456","789"] → "INVALID" (contains digits not rotatable)

Rotate a 3×3 digit grid by 180°

Overview

Problem

Task

Input/Output

Examples

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