Advent of Code 2019, Day 02

aoc_2019_02.rs

use std::env;
use std::fs;

fn run(mut program: Vec<i32>) -> i32 {
    for i in (0..program.len()).step_by(4) {
        let operation = program[i]; // Operation to use, add/mult/break
        let a = program[i+1] as usize;// Index to get first value from
        let b = program[i+2] as usize;// Second value
        let r = program[i+3] as usize;// Index to store result in
        // println!("{} {} {} {}", program[i], program[i+1], program[i+2], program[i+3]);
        match operation {
            1 => { // Add
                program[r] = program[a] + program[b];
            }
            2 => { // Multiply
                program[r] = program[a] * program[b];
            }
            99 => { // Program is finished,
                break; 
            }
            _ => { // Panic on unknown operators, we must have done something wrong then...
                panic!("Unknown operator: {}", program[i]);
            }
        }
    };

    return program[0];
}

fn main() {

    let args: Vec<String> = env::args().collect(); // Get the arguments as a string vector
    let filename = &args[1]; // Where the first passed argument should be the path to the file with inputs,

    let contents = fs::read_to_string(filename)
        .unwrap_or_else(|_| panic!("Failed to read contents of {}", filename));

    let numbers = contents.split(','); // Seeing the numbers this time around is a single line, with comma separated values we will split on ','

    let mut program = Vec::new();
    for number in numbers {
        if number.is_empty(){
            continue;
        }
        let opcode =  number.parse::<i32>();
        let opcode = match opcode {
            Ok(result) => result,
            Err(_error) => { // Let's just throw away the failed parse
                continue;
            }
        };
        program.push(opcode);
    }

    let program_state: Vec<i32> = program.clone(); // Create an immutable copy of the program state,

    // "Restore" the gravity assist program to "1202 program alarm" state
    program[1] = 12;
    program[2] = 2;

    // "Run" the program
    let result = run(program);

    println!("The result from the program is: {}", result);

    let expected_result = 19690720; // The result we are looking for
    for x in 0..99 {
        for y in 0..99 {
            program = program_state.to_vec(); // Restore the program,
            program[1] = x; // Set the 'noun'
            program[2] = y; // Set the 'verb'

            let r = run(program);

            if r == expected_result {
                println!("The value from correct noun and verb pair was {}", 100 * x + y);
            }
        }
    }
}