Refactor day 4 to use Cell enum

README.md

@@ -14,9 +14,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 1](./src/bin/01.rs) | `102.5µs` | `123.5µs` |
 | [Day 2](./src/bin/02.rs) | `45.0ms` | `69.6ms` |
 | [Day 3](./src/bin/03.rs) | `85.1µs` | `121.6µs` |
-| [Day 4](./src/bin/04.rs) | `260.1µs` | `4.0ms` |
+| [Day 4](./src/bin/04.rs) | `244.2µs` | `4.1ms` |
 
-**Total: 119.29ms**
+**Total: 119.38ms**
 <!--- benchmarking table --->
 
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