Day 7

Author: prevostc

README.md

@@ -17,9 +17,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 4](./src/bin/04.rs) | `810.2µs` | `298.7µs` |
 | [Day 5](./src/bin/05.rs) | `67.7µs` | `184.5µs` |
 | [Day 6](./src/bin/06.rs) | `71.1µs` | `24.8ms` |
-| [Day 7](./src/bin/07.rs) | `2.2ms` | `130.7ms` |
+| [Day 7](./src/bin/07.rs) | `2.2ms` | `54.4ms` |
 
-**Total: 161.18ms**
+**Total: 84.88ms**
 <!--- benchmarking table --->
 
 ---

src/bin/07.rs

@@ -54,8 +54,13 @@ impl EquationData {
                     Op::Add => current_value + next_value,
                     Op::Mul => current_value * next_value,
                     Op::Concat => {
-                        let char_count = next_value.to_string().len() as u32;
-                        current_value * 10_u64.pow(char_count) + next_value
+                        let mut digit_count = 0;
+                        let mut n = next_value;
+                        while n > 0 {
+                            digit_count += 1;
+                            n /= 10;
+                        }
+                        current_value * 10_u64.pow(digit_count) + next_value
                     }
                 };