Add solutions for day 4 and 5.1

inputs/day_4.txt

@@ -0,0 +1,141 @@
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+

src/main.rs

@@ -1,3 +1,5 @@
+#![feature(int_roundings)]
+
 mod solutions;
 
 use std::env;
@@ -14,6 +16,8 @@ fn main() -> std::io::Result<()> {
         Ok(1) => solutions::day_1::run(args)?,
         Ok(2) => solutions::day_2::run(args)?,
         Ok(3) => solutions::day_3::run(args)?,
+        Ok(4) => solutions::day_4::run(args)?,
+        Ok(5) => solutions::day_5::run(args)?,
         Ok(_) => eprintln!("Unknown day. Are you from the future?"),
         Err(_) => eprintln!("Unknown day format. Use integers to specify."),
     }

src/solutions/day_4.rs

@@ -0,0 +1,184 @@
+use std::env;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::ops::Add;
+
+enum State {
+    ExpectM,
+    ExpectA,
+    ExpectS,
+}
+
+#[derive(Debug, Copy, Clone)]
+enum Dir {
+    /// Diagonal up left: x - 1, y - 1
+    DiagUL,
+    /// Up: y - 1
+    Up,
+    /// Diagonal up right: x + 1, y - 1
+    DiagUR,
+    /// Left: x - 1
+    Left,
+    /// Right: x + 1
+    Right,
+    /// Diagonal down right: x - 1, y + 1
+    DiagDL,
+    /// Down: y + 1
+    Down,
+    /// Diagonal down right: x + 1, y + 1
+    DiagDR,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+struct Point {
+    x: usize,
+    y: usize,
+}
+
+fn check_direction(map: &Vec<Vec<char>>, state: State, pt: Point, direction: Dir) -> bool {
+    let next_pt = pt + direction;
+
+    let c = map[next_pt.x][next_pt.y];
+
+    match state {
+        State::ExpectM => {
+            if c == 'M' {
+                check_direction(map, State::ExpectA, next_pt, direction)
+            } else {
+                false
+            }
+        }
+        State::ExpectA => {
+            if c == 'A' {
+                check_direction(map, State::ExpectS, next_pt, direction)
+            } else {
+                false
+            }
+        }
+        State::ExpectS => c == 'S',
+    }
+}
+
+fn check_all(map: &Vec<Vec<char>>, x: usize, y: usize) -> u64 {
+    let pt = Point { x, y };
+    let mut sum = 0;
+    if x >= 3 {
+        if y >= 3 && check_direction(map, State::ExpectM, pt, Dir::DiagUL) {
+            sum += 1;
+        }
+        if check_direction(map, State::ExpectM, pt, Dir::Left) {
+            sum += 1;
+        }
+        if (y + 3) < map[0].len() && check_direction(map, State::ExpectM, pt, Dir::DiagDL) {
+            sum += 1;
+        }
+    }
+
+    if y >= 3 && check_direction(map, State::ExpectM, pt, Dir::Up) {
+        sum += 1;
+    }
+    if (y + 3) < map[0].len() && check_direction(map, State::ExpectM, pt, Dir::Down) {
+        sum += 1;
+    }
+
+    if (x + 3) < map.len() {
+        if y >= 3 && check_direction(map, State::ExpectM, pt, Dir::DiagUR) {
+            sum += 1;
+        }
+        if check_direction(map, State::ExpectM, pt, Dir::Right) {
+            sum += 1;
+        }
+        if (y + 3) < map[0].len() && check_direction(map, State::ExpectM, pt, Dir::DiagDR) {
+            sum += 1;
+        }
+    }
+
+    return sum;
+}
+
+fn check_day_2(map: &Vec<Vec<char>>, x: usize, y: usize) -> bool {
+    map[x][y] == 'A'
+        && x >= 1
+        && y >= 1
+        && (x + 1) < map.len()
+        && (y + 1) < map[0].len()
+        && (map[x - 1][y - 1] == 'M' && map[x + 1][y + 1] == 'S'
+            || map[x - 1][y - 1] == 'S' && map[x + 1][y + 1] == 'M')
+        && (map[x - 1][y + 1] == 'M' && map[x + 1][y - 1] == 'S'
+            || map[x - 1][y + 1] == 'S' && map[x + 1][y - 1] == 'M')
+}
+
+pub fn run(mut args: env::Args) -> std::io::Result<()> {
+    let filename = args
+        .next()
+        .expect("You must provide a filename as argument");
+
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+
+    let mut sum = 0;
+    let mut sum_2 = 0;
+    let mut map: Vec<Vec<char>> = Vec::new();
+
+    for line in reader.lines() {
+        let l = line.unwrap();
+        if l.is_empty() {
+            continue;
+        }
+
+        map.push(l.chars().collect());
+    }
+
+    // x: the rows
+    // y: the columns
+    for x in 0..map.len() {
+        for y in 0..map[x].len() {
+            if map[x][y] == 'X' {
+                sum += check_all(&map, x, y);
+            }
+
+            // part 2
+            if check_day_2(&map, x, y) {
+                sum_2 += 1;
+            }
+        }
+    }
+
+    // Task 1
+    println!("Number of 'XMAS': {sum}");
+
+    // Task 2
+    println!("Number of 'X-MAS': {sum_2}");
+
+    Ok(())
+}
+
+impl Add<Dir> for Point {
+    type Output = Self;
+
+    fn add(mut self, other: Dir) -> Self {
+        match other {
+            Dir::Up => self.y -= 1,
+            Dir::Down => self.y += 1,
+            Dir::Left => self.x -= 1,
+            Dir::Right => self.x += 1,
+            Dir::DiagUL => {
+                self.x -= 1;
+                self.y -= 1;
+            }
+            Dir::DiagUR => {
+                self.x += 1;
+                self.y -= 1;
+            }
+            Dir::DiagDL => {
+                self.x -= 1;
+                self.y += 1;
+            }
+            Dir::DiagDR => {
+                self.x += 1;
+                self.y += 1;
+            }
+        }
+        self
+    }
+}

src/solutions/day_5.rs

@@ -0,0 +1,91 @@
+use std::collections::{HashMap, HashSet};
+use std::env;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::str::FromStr;
+
+enum ParserState {
+    Restrictions,
+    Updates,
+}
+
+#[derive(Debug, Default)]
+struct NumEntry {
+    pub less_than: HashSet<u8>,
+    pub greater_than: HashSet<u8>,
+}
+
+pub fn run(mut args: env::Args) -> std::io::Result<()> {
+    let filename = args
+        .next()
+        .expect("You must provide a filename as argument");
+
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+
+    let mut state = ParserState::Restrictions;
+    let mut ordering: HashMap<u8, NumEntry> = HashMap::new();
+    let mut lists: Vec<Vec<u8>> = Vec::new();
+
+    for line in reader.lines() {
+        let l = line.unwrap();
+        match state {
+            ParserState::Restrictions => {
+                if l.is_empty() {
+                    state = ParserState::Updates;
+                } else {
+                    let nums: Vec<u8> =
+                        l.split("|").map(u8::from_str).map(Result::unwrap).collect();
+                    assert!(nums.len() == 2);
+
+                    ordering
+                        .entry(nums[0])
+                        .or_default()
+                        .less_than
+                        .insert(nums[1]);
+                    ordering
+                        .entry(nums[1])
+                        .or_default()
+                        .greater_than
+                        .insert(nums[0]);
+                }
+            }
+            ParserState::Updates => {
+                if !l.is_empty() {
+                    lists.push(l.split(",").map(u8::from_str).map(Result::unwrap).collect());
+                }
+            }
+        }
+    }
+
+    lists.retain(|v| is_compliant(v, &ordering));
+
+    // Task 1
+    let sum = lists.iter().fold(0, |acc, v| {
+        let idx = v.len().div_floor(2);
+        acc + v[idx] as u32
+    });
+
+    println!("Sum of middle values: {sum}");
+
+    // Task 2
+    // TBD
+
+    Ok(())
+}
+
+fn is_compliant(list: &[u8], ordering: &HashMap<u8, NumEntry>) -> bool {
+    for i in 0..list.len() {
+        // skip numbers that have no associated rules
+        if let Some(entry) = ordering.get(&list[i]) {
+            for j in i..list.len() {
+                if entry.greater_than.contains(&list[j]) {
+                    // that's a violation!
+                    return false;
+                }
+            }
+        }
+    }
+
+    return true;
+}

src/solutions/mod.rs

@@ -1,4 +1,6 @@
 pub mod day_1;
 pub mod day_2;
 pub mod day_3;
+pub mod day_4;
+pub mod day_5;