contests/advent_of_code/d3/src/main.rs

use std::io::{self, BufRead};
use std::path::Path;
use std::fs::File;

fn main(){
    // Submarine is breaking, do diagnostics by checking power consumption
    // Calculate gamma rate * epsilon rate
    // Diagnostics are encoded by series of binary numbers

    // Gamma rate is most common bit for each bit in the series
    // Epsilon rate is the opposite, i.e. least common bit

    // So when gamma rate would be 10011, epsilon rate automatically is 01100


    println!("Advent of Code #3!\n");

    let path = Path::new("./3.txt");
    let display = path.display();

    let file = match File::open(&path) {
        Err(why) => panic!("Couldn't open {}: {}", display, why),
        Ok(file) => file,
    };

    let lines = io::BufReader::new(file).lines();
    let mut diagnostics = Vec::<Vec::<bool>>::new();

    for line in lines{
        let mut d_line = Vec::<bool>::new();
        if let Ok(l) = line {
            for c in l.chars() {
                match c {
                    '0' => d_line.push(false),
                    '1' => d_line.push(true),
                    _ => (),
                }
            }
        }
        diagnostics.push(d_line);
    }

    let mut line_numbers = 0;
    let b_len = diagnostics[0].len();
    let mut ones = vec![0; b_len];

    for line in &diagnostics {
        line_numbers += 1;

        for i in 0 .. b_len {
            match line[i] {
                true => ones[i] += 1,
                false => (),
            }
        }
    }

    let mut gamma_rate = Vec::new();
    for n in ones {
        if n > line_numbers / 2 {
            gamma_rate.push(true);
        } else {
            gamma_rate.push(false);
        }
    }

    let mut gamma_rate_decimal = 0;
    let mut pow = 1;

    gamma_rate.reverse();
    for b in &gamma_rate {
        match b {
            true => gamma_rate_decimal += pow,
            false => (),
        }
        pow *= 2;
    }

    println!("Gamma rate in decimal is {}, epsilon rate in decimal is {}, yielding product of {}", 
              gamma_rate_decimal, pow - gamma_rate_decimal - 1, 
              gamma_rate_decimal * (pow - gamma_rate_decimal - 1));



    // Now on to the second part of day 3

    // Verify life support rating, by multiplying oxygen generator rating by co2 scrubber rating
    // Oxygen generator rating is determined by finding the most common bit for the first bit
    // Then, throw out all diagnostics line that do not have the same most common bit for the first position
    // Repeat until only one line remains, this is the oxygen generator rating
    // For the co2 scrubber rating, do the same but for the least common bit per position

    gamma_rate.reverse();
    let mut viable_oxygen = vec![true; line_numbers];
    let mut viable_scrubber = vec![true; line_numbers];

    let mut n_oxygen = line_numbers;
    let mut n_scrubber = line_numbers;

    for bit_n in 0 .. b_len {
        let mcb = most_common_bit(bit_n, &viable_oxygen, &diagnostics);
        let lcb = !most_common_bit(bit_n, &viable_scrubber, &diagnostics);

        for line_n in 0 .. line_numbers {
            if viable_oxygen[line_n] && n_oxygen > 1 {
                if diagnostics[line_n][bit_n] != mcb {
                    n_oxygen -= 1;
                    viable_oxygen[line_n] = false;
                }
            }

            if viable_scrubber[line_n] && n_scrubber > 1 {
                if diagnostics[line_n][bit_n] != lcb {
                    n_scrubber -= 1;
                    viable_scrubber[line_n] = false;
                }
            }
        }

        // println!("\nIteration {}:", bit_n);
        // for line_n in 0 .. line_numbers {
        //     if viable_oxygen[line_n] {
        //         print_bool_vec(&diagnostics[line_n]);
        //     }
        // }

        if n_oxygen == 1 && n_scrubber == 1 {
            break;
        }
    }

    // println!("n_oxygen: {}, n_scrubber: {}", n_oxygen, n_scrubber);

    let mut oxygen_ans = 0;
    let mut scrubber_ans = 0;

    for i in 0 .. line_numbers {
        if viable_oxygen[i] {
            oxygen_ans = i;
        }

        if viable_scrubber[i] {
            scrubber_ans = i;
        }
    }

    print_bool_vec(&diagnostics[oxygen_ans]);
    // print_bool_vec(&diagnostics[scrubber_ans]);

    diagnostics[oxygen_ans].reverse();
    diagnostics[scrubber_ans].reverse();

    let oxygen_dec = bit_to_decimal(&diagnostics[oxygen_ans]);
    let scrubber_dec = bit_to_decimal(&diagnostics[scrubber_ans]);

    println!("Oxygen generator rating is {}, co2 scrubber rating is {}, yields product of {}",
              oxygen_dec, scrubber_dec, oxygen_dec * scrubber_dec);
}

fn bit_to_decimal(bits: &Vec::<bool>) -> u64 {
    let mut pow = 1;
    let mut result = 0;

    for b in bits {
        match b {
            true => result += pow,
            false => (),
        }
        pow *= 2;
    }

    return result;
}

fn most_common_bit(index: usize, valid_series: &Vec::<bool>, bit_series: &Vec::<Vec::<bool>>) -> bool {
    let mut ones = 0;
    let mut valids = 0;
    
    for i in 0 .. valid_series.len() {
        if valid_series[i] {
            valids += 1;

            if bit_series[i][index] {
                ones += 1;
            }
        }
    }

    let mut v = valids as f32;
    v /= 2.0;
    v = v.ceil();
    valids = v as u64;

    if ones >= valids {
        return true;
    }

    return false;
}

fn print_bool_vec(input: &Vec::<bool>) -> () {
    for b in input {
        print!("{},", b);
    } println!();
}