GPT-5.6 Sol vs Grok 4.5 for coding

```regex
/^(?:GIR ?0AA|[A-PR-UWYZ](?:[0-9][0-9A-HJKSTUW]?|[A-HK-Y][0-9][0-9ABEHMNPRVWXY]?) ?[0-9][ABD-HJLNP-UW-Z]{2})$/i
```

- `^` and `$` — require the entire input to match.
- `GIR ?0AA` — handles the exceptional postcode `GIR 0AA`, with an optional space.
- `[A-PR-UWYZ]` — matches an allowed first postcode-area letter.
- `[0-9][0-9A-HJKSTUW]?` — matches districts for a one-letter area, such as `M1`, `M60`, or `W1A`.
- `[A-HK-Y][0-9][0-9ABEHMNPRVWXY]?` — matches a second area letter and district, such as `SW1` or `EC1A`.
- ` ?` — permits zer…

**Regex:** `/^[A-Z]{1,2}\d[A-Z\d]? ?\d[A-Z]{2}$/i`

- `^` — start of string  
- `[A-Z]{1,2}` — 1–2 letters (area)  
- `\d` — one digit (district start)  
- `[A-Z\d]?` — optional letter or digit (rest of district)  
- ` ?` — optional space  
- `\d` — one digit (sector)  
- `[A-Z]{2}` — two letters (unit)  
- `$` — end of string  
- `i` flag — case-insensitive  

Two valid UK postcodes this would reject: `EC1A 1BB` (the `A` after the digit in the outward code is only partially covered by the optional class in some edge positions), `W1A 0AX` (same…