feat: day 4

inputs/day04/example.txt

@@ -0,0 +1,10 @@
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX

src/day04.rs

@@ -0,0 +1,130 @@
+pub fn pt1(input: &str) -> usize {
+    let lines = input
+        .lines()
+        .map(|l| l.chars().collect::<Vec<_>>())
+        .collect::<Vec<_>>();
+    let mut count = 0;
+    for (i, line) in lines.iter().enumerate() {
+        for (j, c) in line.iter().enumerate() {
+            if *c == 'X' {
+                if j >= 3
+                    && line.get(j.saturating_sub(1)) == Some(&'M')
+                    && line.get(j.saturating_sub(2)) == Some(&'A')
+                    && line.get(j.saturating_sub(3)) == Some(&'S')
+                {
+                    count += 1;
+                }
+                if j + 3 <= line.len()
+                    && line.get(j + 1) == Some(&'M')
+                    && line.get(j + 2) == Some(&'A')
+                    && line.get(j + 3) == Some(&'S')
+                {
+                    count += 1;
+                }
+                if i >= 3
+                    && lines.get(i.saturating_sub(1)).and_then(|l| l.get(j)) == Some(&'M')
+                    && lines.get(i.saturating_sub(2)).and_then(|l| l.get(j)) == Some(&'A')
+                    && lines.get(i.saturating_sub(3)).and_then(|l| l.get(j)) == Some(&'S')
+                {
+                    count += 1;
+                }
+                if i + 3 <= lines.len()
+                    && lines.get(i + 1).and_then(|l| l.get(j)) == Some(&'M')
+                    && lines.get(i + 2).and_then(|l| l.get(j)) == Some(&'A')
+                    && lines.get(i + 3).and_then(|l| l.get(j)) == Some(&'S')
+                {
+                    count += 1;
+                }
+                if i >= 3
+                    && j >= 3
+                    && lines
+                        .get(i.saturating_sub(1))
+                        .and_then(|l| l.get(j.saturating_sub(1)))
+                        == Some(&'M')
+                    && lines
+                        .get(i.saturating_sub(2))
+                        .and_then(|l| l.get(j.saturating_sub(2)))
+                        == Some(&'A')
+                    && lines
+                        .get(i.saturating_sub(3))
+                        .and_then(|l| l.get(j.saturating_sub(3)))
+                        == Some(&'S')
+                {
+                    count += 1;
+                }
+                if i >= 3
+                    && j + 3 <= line.len()
+                    && lines.get(i.saturating_sub(1)).and_then(|l| l.get(j + 1)) == Some(&'M')
+                    && lines.get(i.saturating_sub(2)).and_then(|l| l.get(j + 2)) == Some(&'A')
+                    && lines.get(i.saturating_sub(3)).and_then(|l| l.get(j + 3)) == Some(&'S')
+                {
+                    count += 1;
+                }
+                if j >= 3
+                    && i + 3 <= lines.len()
+                    && lines.get(i + 1).and_then(|l| l.get(j.saturating_sub(1))) == Some(&'M')
+                    && lines.get(i + 2).and_then(|l| l.get(j.saturating_sub(2))) == Some(&'A')
+                    && lines.get(i + 3).and_then(|l| l.get(j.saturating_sub(3))) == Some(&'S')
+                {
+                    count += 1;
+                }
+                if j + 3 <= line.len()
+                    && i + 3 <= lines.len()
+                    && lines.get(i + 1).and_then(|l| l.get(j + 1)) == Some(&'M')
+                    && lines.get(i + 2).and_then(|l| l.get(j + 2)) == Some(&'A')
+                    && lines.get(i + 3).and_then(|l| l.get(j + 3)) == Some(&'S')
+                {
+                    count += 1;
+                }
+            }
+        }
+    }
+    count
+}
+
+pub fn pt2(input: &str) -> usize {
+    let lines = input
+        .lines()
+        .map(|l| l.chars().collect::<Vec<_>>())
+        .collect::<Vec<_>>();
+    let mut count = 0;
+    for (i, line) in lines.iter().enumerate() {
+        for (j, c) in line.iter().enumerate() {
+            if *c == 'A' && (j >= 1 && i >= 1 && j + 1 < line.len() && i + 1 < lines.len()) {
+                let top_left = lines.get(i - 1).and_then(|l| l.get(j - 1));
+                let bottom_right = lines.get(i + 1).and_then(|l| l.get(j + 1));
+                let bottom_left = lines.get(i + 1).and_then(|l| l.get(j - 1));
+                let top_right = lines.get(i - 1).and_then(|l| l.get(j + 1));
+                if ((top_left == Some(&'M') && bottom_right == Some(&'S'))
+                    || (top_left == Some(&'S') && bottom_right == Some(&'M')))
+                    && ((bottom_left == Some(&'M') && top_right == Some(&'S'))
+                        || (bottom_left == Some(&'S') && top_right == Some(&'M')))
+                {
+                    count += 1;
+                }
+            }
+        }
+    }
+    count
+}
+
+#[cfg(test)]
+mod tests {
+    use std::fs::read_to_string;
+
+    use super::{pt1, pt2};
+
+    #[test]
+    pub fn test_pt1() {
+        let input =
+            read_to_string("./inputs/day04/example.txt").expect("Missing example.txt for day04");
+        assert_eq!(pt1(&input), 18)
+    }
+    #[test]
+    pub fn test_pt2() {
+        let input =
+            read_to_string("./inputs/day04/example.txt").expect("Missing example_2.txt for day04");
+
+        assert_eq!(pt2(&input), 9)
+    }
+}

src/main.rs

@@ -3,12 +3,14 @@ use std::{fmt::Display, fs::read_to_string, time::Instant};
 mod day01;
 mod day02;
 mod day03;
+mod day04;
 fn main() {
     color_eyre::install().unwrap();
     tracing_subscriber::fmt::init();
     solve_day(1, day01::pt1, day01::pt2);
     solve_day(2, day02::pt1, day02::pt2);
     solve_day(3, day03::pt1, day03::pt2);
+    solve_day(4, day04::pt1, day04::pt2);
 }
 
 fn solve_day<Fa, Fb, Ta, Tb>(day: u8, part_a: Fa, part_b: Fb)