AoC2021/src/day3.rs

use std::fs;

pub fn run() {
    println!("Day 3:");
    let input = fs::read_to_string("./inputs/day3.txt").expect("Could not read file");

    let report: Vec<&str> = input.lines().collect();
    let bit_count = report[0].len();

    {
        // Part 1
        let col_size = report.len();

        let mut gamma = 0;
        let mut epsilon = 0;

        for position in 0..bit_count {
            gamma <<= 1;
            epsilon <<= 1;

            let count = report
                .iter()
                .filter(|b| b.chars().nth(position).unwrap() == '1')
                .count();

            if count > col_size / 2 {
                gamma += 1;
            } else {
                epsilon += 1;
            }
        }
        println!("\tPart 1: {}", gamma * epsilon);
    }

    {
        // Part 2
        let generator: i32 = {
            let mut diagnostic = report.to_vec();

            for position in 0..bit_count {
                let col_size = diagnostic.len();
                let count = diagnostic
                    .iter()
                    .filter(|b| b.chars().nth(position).unwrap() == '1')
                    .count();

                if count >= (col_size - count) {
                    diagnostic.retain(|b| b.chars().nth(position).unwrap() == '1');
                } else {
                    diagnostic.retain(|b| b.chars().nth(position).unwrap() == '0');
                }

                if diagnostic.len() == 1 {
                    break;
                }
            }
            i32::from_str_radix(diagnostic[0], 2).unwrap()
        };

        let scrubber = {
            let mut diagnostic = report.to_vec();

            for position in 0..bit_count {
                let col_size = diagnostic.len();
                let count = diagnostic
                    .iter()
                    .filter(|b| b.chars().nth(position).unwrap() == '0')
                    .count();

                if count > (col_size - count) {
                    diagnostic.retain(|b| b.chars().nth(position).unwrap() == '1');
                } else {
                    diagnostic.retain(|b| b.chars().nth(position).unwrap() == '0');
                }

                if diagnostic.len() == 1 {
                    break;
                }
            }
            i32::from_str_radix(diagnostic[0], 2).unwrap()
        };

        println!("\tPart 2: {}", generator * scrubber);
    }
}