From ed5ac4446c07157fec1cb93cf572601a15c1be38 Mon Sep 17 00:00:00 2001
From: Rh4096 <rhelvetican@gmail.com>
Date: Wed, 4 Dec 2024 20:07:33 +0700
Subject: [PATCH] day 4

---
 src/lib.rs             |   1 +
 src/main.rs            |   4 +-
 src/solutions/day_4.rs | 104 +++++++++++++++++++++++++++++++++++++++++
 src/utils/mod.rs       |   1 +
 4 files changed, 108 insertions(+), 2 deletions(-)
 create mode 100644 src/utils/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index 3242762..d952180 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1,2 @@
 pub mod solutions;
+pub mod utils;
diff --git a/src/main.rs b/src/main.rs
index ba7a4b2..61f92a8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,7 +1,7 @@
-use aoc2024::solutions::{day_3::AocDayThreeSolution, AocSolution};
+use aoc2024::solutions::{day_4::AocDayFourSolution, AocSolution};
 
 fn main() {
-    let sol = AocDayThreeSolution;
+    let sol = AocDayFourSolution;
 
     println!("p1: {}\np2: {}", sol.part_one(), sol.part_two())
 }
diff --git a/src/solutions/day_4.rs b/src/solutions/day_4.rs
index e69de29..d973ee5 100644
--- a/src/solutions/day_4.rs
+++ b/src/solutions/day_4.rs
@@ -0,0 +1,104 @@
+use std::collections::HashMap;
+
+use super::AocSolution;
+
+const DIRS: [(i16, i16); 8] = [
+    (1, 0),
+    (1, -1),
+    (0, -1),
+    (-1, -1),
+    (-1, 0),
+    (-1, 1),
+    (0, 1),
+    (1, 1),
+];
+
+struct XmasGrid {
+    pub grid: HashMap<(i16, i16), char>,
+}
+
+impl XmasGrid {
+    fn new(src: &str) -> Self {
+        Self {
+            grid: src
+                .lines()
+                .zip(0..)
+                .flat_map(|(l, y)| l.chars().zip(0..).map(move |(c, x)| ((x, y), c)))
+                .collect(),
+        }
+    }
+
+    fn find_xmas(&self, pos: (i16, i16)) -> usize {
+        let mut tmp = 0;
+        for (dx, dy) in DIRS {
+            let mut found = true;
+            let (mut x, mut y) = pos;
+
+            for nxt in ['M', 'A', 'S'] {
+                x += dx;
+                y += dy;
+
+                if self.grid.get(&(x, y)) != Some(&nxt) {
+                    found = false;
+                    break;
+                }
+            }
+
+            if found {
+                tmp += 1;
+            }
+        }
+
+        tmp
+    }
+
+    fn find_x_mas(&self, pos: (i16, i16)) -> usize {
+        let (x, y) = pos;
+
+        let tr = self.grid.get(&(x + 1, y + 1));
+        let br = self.grid.get(&(x + 1, y - 1));
+        let bl = self.grid.get(&(x - 1, y - 1));
+        let tl = self.grid.get(&(x - 1, y + 1));
+
+        match (tr, bl, tl, br) {
+            (Some('S'), Some('M'), Some('M'), Some('S')) => 1,
+            (Some('M'), Some('S'), Some('S'), Some('M')) => 1,
+            (Some('S'), Some('M'), Some('S'), Some('M')) => 1,
+            (Some('M'), Some('S'), Some('M'), Some('S')) => 1,
+            _ => 0,
+        }
+    }
+}
+
+pub struct AocDayFourSolution;
+
+impl AocSolution for AocDayFourSolution {
+    type Output = usize;
+    const INPUT: &str = include_str!("../../input/day4.txt");
+
+    fn part_one(&self) -> Self::Output {
+        let xmas = XmasGrid::new(Self::INPUT);
+        let mut tmp = 0;
+
+        for (&pos, &ch) in &xmas.grid {
+            if ch == 'X' {
+                tmp += xmas.find_xmas(pos)
+            }
+        }
+
+        tmp as Self::Output
+    }
+
+    fn part_two(&self) -> Self::Output {
+        let xmas = XmasGrid::new(Self::INPUT);
+        let mut tmp = 0;
+
+        for (&pos, &ch) in &xmas.grid {
+            if ch == 'A' {
+                tmp += xmas.find_x_mas(pos)
+            }
+        }
+
+        tmp as Self::Output
+    }
+}
diff --git a/src/utils/mod.rs b/src/utils/mod.rs
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/src/utils/mod.rs
@@ -0,0 +1 @@
+