My submissions for Advent of Code 2025
adventofcode.com/2025
cherry.computer
rust
aoc
1use std::{fs::read_to_string, iter};
2
3fn main() {
4 let input = read_to_string("../input.txt").expect("failed to open input file");
5 let mut problems = input.lines();
6 let operator_line = problems.next_back().expect("file was empty");
7 let numbers: Vec<_> = problems.collect();
8
9 let operators: Vec<_> = operator_line.match_indices(['+', '*']).collect();
10 let last_operator = operators.last().expect("couldn't find any operators");
11
12 let grand_total: u64 = operators
13 .windows(2)
14 .map(|window| (window[0].0..window[1].0 - 1, window[0].1))
15 .chain(iter::once((
16 last_operator.0..operator_line.len(),
17 last_operator.1,
18 )))
19 .map(|(problem_range, operator)| {
20 let numbers = problem_range.map(|column| {
21 numbers
22 .iter()
23 .filter_map(|number_line| (number_line.as_bytes()[column] as char).to_digit(10))
24 .rev()
25 .enumerate()
26 .map(|(placement, digit)| u64::from(digit) * 10u64.pow(placement as u32))
27 .sum::<u64>()
28 });
29 match operator {
30 "+" => numbers.sum::<u64>(),
31 "*" => numbers.product(),
32 operator => panic!("unrecognised operator '{operator}'"),
33 }
34 })
35 .sum();
36 println!("The grand total is {grand_total}!");
37}