Rotate a 3×3 digit grid by 180°

## 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**: 1. Each cell `(r, c)` moves to `(2 - r, 2 - c)`. 2. 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)