Add day4

day4/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day4"
+version = "0.1.0"

day4/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day4"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day4/src/main.rs

@@ -0,0 +1,109 @@
+fn parse(input: &str) -> Vec<Vec<char>> {
+    input.lines().map(|line| line.chars().collect()).collect()
+}
+
+fn part1(input: &[Vec<char>]) -> u32 {
+    let xmas = ['X', 'M', 'A', 'S'];
+    let directions: [(i32, i32); 8] = [
+        (0, 1),
+        (0, -1),
+        (1, 0),
+        (-1, 0),
+        (1, 1),
+        (-1, -1),
+        (1, -1),
+        (-1, 1),
+    ];
+    input
+        .iter()
+        .enumerate()
+        .map(|(line_idx, line)| {
+            line.iter()
+                .enumerate()
+                .map(|(col_idx, c)| {
+                    if c != &xmas[0] {
+                        return 0;
+                    }
+                    directions
+                        .iter()
+                        .map(|(dir_x, dir_y)| {
+                            xmas.iter()
+                                .enumerate()
+                                .skip(1)
+                                .fold(1, |acc, (shift, xmas_char)| {
+                                    let Some(Some(cc)) = input
+                                        .get((line_idx as i32 + (dir_y * (shift as i32))) as usize)
+                                        .map(|ll| {
+                                            ll.get(
+                                                (col_idx as i32 + dir_x * (shift as i32)) as usize,
+                                            )
+                                        })
+                                    else {
+                                        return 0;
+                                    };
+                                    if cc != xmas_char {
+                                        return 0;
+                                    }
+                                    acc
+                                })
+                        })
+                        .sum::<u32>()
+                })
+                .sum::<u32>()
+        })
+        .sum()
+}
+
+fn part2(input: &[Vec<char>]) -> u32 {
+    input
+        .iter()
+        .enumerate()
+        .map(|(line_idx, line)| {
+            line.iter()
+                .enumerate()
+                .map(|(col_idx, c)| {
+                    if c != &'A' {
+                        return 0;
+                    }
+                    let Some(Some(up_left)) = input
+                        .get(line_idx.overflowing_sub(1).0)
+                        .map(|l| l.get(col_idx.overflowing_sub(1).0))
+                    else {
+                        return 0;
+                    };
+                    let Some(Some(up_right)) = input
+                        .get(line_idx.overflowing_sub(1).0)
+                        .map(|l| l.get(col_idx + 1))
+                    else {
+                        return 0;
+                    };
+                    let Some(Some(down_left)) = input
+                        .get(line_idx + 1)
+                        .map(|l| l.get(col_idx.overflowing_sub(1).0))
+                    else {
+                        return 0;
+                    };
+                    let Some(Some(down_right)) =
+                        input.get(line_idx + 1).map(|l| l.get(col_idx + 1))
+                    else {
+                        return 0;
+                    };
+                    if ((up_left == &'M' && down_right == &'S')
+                        || (up_left == &'S' && down_right == &'M'))
+                        && ((up_right == &'M' && down_left == &'S')
+                            || (up_right == &'S' && down_left == &'M'))
+                    {
+                        1
+                    } else {
+                        0
+                    }
+                })
+                .sum::<u32>()
+        })
+        .sum()
+}
+fn main() {
+    let input = parse(include_str!("../input.txt"));
+    println!("{}", part1(&input));
+    println!("{}", part2(&input));
+}