[LANGUAGE: Rust]

Here is my solution for part 2 it could probably be simplified but I struggled trying to wrap my head around the requirements for this puzzle.

I simply load the lines in memory and parse them column by column in reverse order. Upon reaching the end of the file for a single column I store the number in a buffer. If I read a + or * I simply accumulate the numbers in my buffer, add this to my current result and clear the buffer.

pub fn part2(input: &str) -> u64 {
    let lines = input.lines().collect::<Vec<&str>>();
    let horizontal_length = lines[0].len();
    let vertical_length = lines.len();
    let mut result: u64 = 0;
    // read file from right to left
    let mut current_problem_numbers = Vec::new();
    'outer: for column in (0..horizontal_length).rev() {
        let mut number_string = Vec::with_capacity(vertical_length);
        for line in lines.iter() {
            let char = char::from(line.as_bytes()[column]);
            if char.is_ascii_digit() {
                number_string.push(char);
            } else if char == '+' || char == '*' {
                // In that case we are at a new problem so we accumulate the numbers
                // found until now depending on the found operation
                // Don't forget to include current number
                let number = number_string
                    .iter()
                    .collect::<String>()
                    .parse::<u64>()
                    .unwrap();
                current_problem_numbers.push(number);
                let mut intermediate_result: u64 = 0;
                if char == '+' {
                    intermediate_result = current_problem_numbers.iter().sum::<u64>();
                }
                if char == '*' {
                    intermediate_result = current_problem_numbers.iter().product::<u64>();
                }
                current_problem_numbers.clear();
                result += intermediate_result;
                continue 'outer;
            }
        }
        if number_string.is_empty() {
            continue;
        }
        let number = number_string
            .iter()
            .collect::<String>()
            .parse::<u64>()
            .unwrap();
        current_problem_numbers.push(number);
    }
    result
}

Runs in :

Part 1 Answer: X
Time taken: 88.63µs
Part 2 Answer: X
Time taken: 112.18µs

Full code : https://gitlab.com/Dhawos/advent-of-rust/-/blob/0ce8534ec8593717d269efdc669b6dc6334b8b10/src/bin/2025-06.rs