From 33472462bd78178ee9e2f870583cbef0a45fe7fc Mon Sep 17 00:00:00 2001
From: Louis Vallat <contact@louis-vallat.fr>
Date: Wed, 4 Dec 2024 23:45:24 +0100
Subject: [PATCH] feat: added day 4 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.fr>
---
 .gitea/workflows/build_and_run.yml |   2 +-
 day4/Cargo.toml                    |   6 ++
 day4/src/main.rs                   | 101 +++++++++++++++++++++++++++++
 3 files changed, 108 insertions(+), 1 deletion(-)
 create mode 100644 day4/Cargo.toml
 create mode 100644 day4/src/main.rs

diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index 8a30cbe..dd96060 100644
--- a/.gitea/workflows/build_and_run.yml
+++ b/.gitea/workflows/build_and_run.yml
@@ -11,7 +11,7 @@ jobs:
     name: Challenge for day
     strategy:
       matrix:
-        day_number: [1, 2, 3]
+        day_number: [1, 2, 3, 4]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day4/Cargo.toml b/day4/Cargo.toml
new file mode 100644
index 0000000..0ebbbc8
--- /dev/null
+++ b/day4/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day4"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day4/src/main.rs b/day4/src/main.rs
new file mode 100644
index 0000000..c656e97
--- /dev/null
+++ b/day4/src/main.rs
@@ -0,0 +1,101 @@
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> Vec<Vec<char>> {
+    input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| line.chars().collect())
+        .collect()
+}
+
+fn has_word(
+    word: &str,
+    matrix: &Vec<Vec<char>>,
+    source: (usize, usize),
+    direction: (i32, i32),
+) -> bool {
+    let word = word.chars().collect::<Vec<char>>();
+    let (row, col) = source;
+    let (i_row, i_col, i_word_len) = (row as i32, col as i32, word.len() as i32);
+
+    if !(0..matrix.len() as i32).contains(&(i_row + ((i_word_len - 1) * direction.0)))
+        || !(0..matrix[row].len() as i32).contains(&(i_col + ((i_word_len - 1) * direction.1)))
+    {
+        return false;
+    }
+
+    for (offset, c) in word.iter().enumerate() {
+        let i_offset = offset as i32;
+        if matrix[(i_row + i_offset * direction.0) as usize]
+            [(i_col + i_offset * direction.1) as usize]
+            != *c
+        {
+            return false;
+        }
+    }
+    true
+}
+
+fn part_1(matrix: &Vec<Vec<char>>) -> u32 {
+    let mut found = 0;
+    for (row, line) in matrix.iter().enumerate() {
+        for (col, c) in line.iter().enumerate() {
+            if *c != 'X' {
+                continue;
+            }
+
+            for i in -1..=1 {
+                for j in -1..=1 {
+                    if i == 0 && j == 0 {
+                        continue;
+                    }
+
+                    if has_word("XMAS", matrix, (row, col), (i, j)) {
+                        found += 1;
+                    }
+                }
+            }
+        }
+    }
+    found
+}
+
+fn is_mas(matrix: &Vec<Vec<char>>, row: usize, col: usize, flag: bool) -> bool {
+    if matrix[row][col] != 'A' {
+        return false;
+    }
+    if flag {
+        (matrix[row - 1][col - 1] == 'M' && matrix[row + 1][col + 1] == 'S')
+            || (matrix[row - 1][col - 1] == 'S' && matrix[row + 1][col + 1] == 'M')
+    } else {
+        (matrix[row + 1][col - 1] == 'M' && matrix[row - 1][col + 1] == 'S')
+            || (matrix[row + 1][col - 1] == 'S' && matrix[row - 1][col + 1] == 'M')
+    }
+}
+
+fn part_2(matrix: &Vec<Vec<char>>) -> u32 {
+    let mut found = 0;
+    for row in 1..(matrix.len() - 1) {
+        for col in 1..(matrix[row].len() - 1) {
+            if is_mas(matrix, row, col, true) && is_mas(matrix, row, col, false) {
+                found += 1;
+            }
+        }
+    }
+    found
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let matrix = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&matrix));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&matrix));
+    }
+}