Add solution for 2020 day 02

2020/README.md

@@ -5,7 +5,7 @@
 | Day | Part 1 | Part 2 | Language |
 | :-: | :----: | :----: | :------- |
 | 01  |   ✓    |   ✓    | Rust     |
-| 02  |        |        |          |
+| 02  |   ✓    |   ✓    | Rust     |
 | 03  |        |        |          |
 | 04  |        |        |          |
 | 05  |        |        |          |

2020/day-02/.gitignore

@@ -0,0 +1,2 @@
+part_one
+part_two

2020/day-02/common.rs

@@ -0,0 +1,30 @@
+use std::env;
+use std::fs::File;
+use std::io::Read;
+
+pub type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
+
+pub fn read_file() -> Result<Vec<(usize, usize, char, String)>> {
+    let path = env::args().skip(1).next().unwrap();
+    let mut file = File::open(path)?;
+    let mut content = String::new();
+    file.read_to_string(&mut content)?;
+
+    let result = content
+        .lines()
+        .map(|line| {
+            let tokens = line
+                .split(&[' ', ':', '-'][..])
+                .filter(|&x| x != "")
+                .collect::<Vec<_>>();
+            (
+                tokens[0].parse().unwrap(),
+                tokens[1].parse().unwrap(),
+                tokens[2].chars().next().unwrap(),
+                tokens[3].into(),
+            )
+        })
+        .collect();
+
+    Ok(result)
+}

2020/day-02/inputs/sample.txt

@@ -0,0 +1,3 @@
+1-3 a: abcde
+1-3 b: cdefg
+2-9 c: ccccccccc

2020/day-02/part_one.rs

@@ -0,0 +1,33 @@
+mod common;
+
+use common::{read_file, Result};
+
+fn main() -> Result<()> {
+    let entries = read_file()?;
+
+    let mut valid_passwords = 0;
+
+    'entries: for (min, max, req_char, password) in entries {
+        let mut char_counter = 0;
+
+        for character in password.chars() {
+            if character == req_char {
+                char_counter += 1;
+            }
+
+            if char_counter > max {
+                continue 'entries;
+            }
+        }
+
+        if char_counter < min {
+            continue;
+        }
+
+        valid_passwords += 1;
+    }
+
+    println!("{}", valid_passwords);
+
+    Ok(())
+}

2020/day-02/part_two.rs

@@ -0,0 +1,22 @@
+mod common;
+
+use common::{read_file, Result};
+
+fn main() -> Result<()> {
+    let entries = read_file()?;
+
+    let mut valid_passwords = 0;
+
+    for (pos1, pos2, req_char, password) in entries {
+        let a = password.chars().nth(pos1 - 1).unwrap() == req_char;
+        let b = password.chars().nth(pos2 - 1).unwrap() == req_char;
+
+        if a ^ b {
+            valid_passwords += 1;
+        }
+    }
+
+    println!("{}", valid_passwords);
+
+    Ok(())
+}