AdventOfCode/day2/src/main.rs

use std::fs::File;
use std::io::Read;
use std::prelude::v1::Vec;
use std::collections::HashMap;

fn main() {
    let mut f = File::open("input").expect("file not found");

    let mut contents = String::new();
    f.read_to_string(&mut contents).expect("something went wrong reading the file");

    let lines: Vec<&str> = contents.split("\n").collect();

    println!("{}", count_doubles_and_triples(&lines));

    let common_letters : String;

    match find_common_letters(&lines){
        Ok(s) => common_letters = s.into_iter().collect(),
        Err(s) => common_letters = s.to_string(),
    }

    println!("{}", common_letters);
}

fn count_doubles_and_triples(lines: &Vec<&str>) -> i32 {
    let mut doubles = 0;
    let mut triples = 0;

    for line in lines {
        let mut counts = HashMap::new();

        for character in line.chars() {
            *counts.entry(character).or_insert(0) += 1;
        }

        if counts.values().any(|&count| count == 2) {
            doubles += 1;
        }

        if counts.values().any(|&count| count == 3) {
            triples += 1;
        }
    }

    triples * doubles
}

fn find_common_letters(lines: &Vec<&str>) -> Result<Vec<char> , std::io::Error> {
    for line in lines {
        for line2 in lines {
            let mismatches = line.chars().zip(line2.chars()).filter(|&(a, b)| a != b).count();

            if mismatches == 1 {
                let result: Vec<(char,char)> = line.chars().zip(line2.chars()).filter(|&(a, b)| a == b).collect();

                let candidate1: Vec<char> = line.chars().collect();
                let candidate2: Vec<char> = line2.chars().collect();

                let mut result: Vec<char> = Vec::new();

                for x in 0..candidate1.len() {
                    if candidate1[x] == candidate2[x]{
                        result.push(candidate1[x]);
                    }
                }

                return Ok(test);
            }
        }
    }


    Err(std::io::Error::new(std::io::ErrorKind::Other, "No match found"))
}