AoC24: Solve day 4 part 1

advent-of-code-2024/src/day04.rs

@@ -0,0 +1,212 @@
+// --- Day 4: Ceres Search ---
+
+// "Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
+
+// As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her with her word search (your puzzle input). She only has to find one word: XMAS.
+
+// This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little unusual, though, as you don't merely need to find one instance of XMAS - you need to find all of them. Here are a few ways XMAS might appear, where irrelevant characters have been replaced with .:
+
+// ..X...
+// .SAMX.
+// .A..A.
+// XMAS.S
+// .X....
+
+// The actual word search will be full of letters instead. For example:
+
+// MMMSXXMASM
+// MSAMXMSMSA
+// AMXSXMAAMM
+// MSAMASMSMX
+// XMASAMXAMM
+// XXAMMXXAMA
+// SMSMSASXSS
+// SAXAMASAAA
+// MAMMMXMMMM
+// MXMXAXMASX
+
+// In this word search, XMAS occurs a total of 18 times; here's the same word search again, but where letters not involved in any XMAS have been replaced with .:
+
+// ....XXMAS.
+// .SAMXMS...
+// ...S..A...
+// ..A.A.MS.X
+// XMASAMX.MM
+// X.....XA.A
+// S.S.S.S.SS
+// .A.A.A.A.A
+// ..M.M.M.MM
+// .X.X.XMASX
+
+// Take a look at the little Elf's word search. How many times does XMAS appear?
+
+// --- Part Two ---
+
+// The Elf looks quizzically at you. Did you misunderstand the assignment?
+
+// Looking for the instructions, you flip over the word search to find that this isn't actually an XMAS puzzle; it's an X-MAS puzzle in which you're supposed to find two MAS in the shape of an X. One way to achieve that is like this:
+
+// M.S
+// .A.
+// M.S
+
+// Irrelevant characters have again been replaced with . in the above diagram. Within the X, each MAS can be written forwards or backwards.
+
+// Here's the same example from before, but this time all of the X-MASes have been kept instead:
+
+// .M.S......
+// ..A..MSMS.
+// .M.S.MAA..
+// ..A.ASMSM.
+// .M.S.M....
+// ..........
+// S.S.S.S.S.
+// .A.A.A.A..
+// M.M.M.M.M.
+// ..........
+
+// In this example, an X-MAS appears 9 times.
+
+// Flip the word search from the instructions back over to the word search side and try again. How many times does an X-MAS appear?
+
+
+#[allow(clippy::cast_possible_wrap)]
+fn try_right(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x + 3 >= matrix[y].len() {
+        return false;
+    }
+
+    matrix[y][x + 1] == 'M' && matrix[y][x + 2] == 'A' && matrix[y][x + 3] == 'S'
+}
+
+#[allow(clippy::cast_possible_wrap)]
+fn try_left(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if (x as isize) - 3 < 0 {
+        return false;
+    }
+
+    matrix[y][x - 1] == 'M' && matrix[y][x - 2] == 'A' && matrix[y][x - 3] == 'S'
+}
+
+#[allow(clippy::cast_possible_wrap)]
+fn try_down(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if y + 3 >= matrix.len() {
+        return false;
+    }
+
+    matrix[y + 1][x] == 'M' && matrix[y + 2][x] == 'A' && matrix[y + 3][x] == 'S'
+}
+
+#[allow(clippy::cast_possible_wrap)]
+fn try_up(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if (y as isize) - 3 < 0 {
+        return false;
+    }
+
+    matrix[y - 1][x] == 'M' && matrix[y - 2][x] == 'A' && matrix[y - 3][x] == 'S'
+}
+#[allow(clippy::cast_possible_wrap)]
+fn try_right_down(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x + 3 >= matrix[y].len() || y + 3 >= matrix.len() {
+        return false;
+    }
+
+    matrix[y + 1][x + 1] == 'M' && matrix[y + 2][x + 2] == 'A' && matrix[y + 3][x + 3] == 'S'
+}
+
+#[allow(clippy::cast_possible_wrap)]
+fn try_left_down(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if (x as isize) - 3 < 0 || y + 3 >= matrix.len() {
+        return false;
+    }
+
+    matrix[y + 1][x - 1] == 'M' && matrix[y + 2][x - 2] == 'A' && matrix[y + 3][x - 3] == 'S'
+}
+#[allow(clippy::cast_possible_wrap)]
+fn try_right_up(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x + 3 >= matrix[y].len() || (y as isize) - 3 < 0 {
+        return false;
+    }
+
+    matrix[y - 1][x + 1] == 'M' && matrix[y - 2][x + 2] == 'A' && matrix[y - 3][x + 3] == 'S'
+}
+#[allow(clippy::cast_possible_wrap)]
+fn try_left_up(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if (x as isize) - 3 < 0 || (y as isize) - 3 < 0 {
+        return false;
+    }
+
+    matrix[y - 1][x - 1] == 'M' && matrix[y - 2][x - 2] == 'A' && matrix[y - 3][x - 3] == 'S'
+}
+
+// It returs the number of XMAS found
+fn find_xmas(matrix: &[Vec<char>], x: usize, y: usize) -> u32 {
+    let r = try_right(matrix, x, y);
+    let l = try_left(matrix, x, y);
+    let d = try_down(matrix, x, y);
+    let u = try_up(matrix, x, y);
+    let rd = try_right_down(matrix, x, y);
+    let ld = try_left_down(matrix, x, y);
+    let ru = try_right_up(matrix, x, y);
+    let lu = try_left_up(matrix, x, y);
+
+    r as u32 + l as u32 + d as u32 + u as u32 + rd as u32 + ld as u32 + ru as u32 + lu as u32
+}
+
+#[must_use]
+pub fn solve(input: &str) -> (u32, u32) {
+    let matrix = input
+        .lines()
+        .map(|line| line.chars().collect::<Vec<_>>())
+        .collect::<Vec<_>>();
+
+    let mut p1 = 0;
+    let (mut x, mut y) = (0, 0);
+
+    let horizontal_len = matrix[0].len();
+    let vertical_len = matrix.len();
+
+    loop {
+        if y >= vertical_len {
+            // finished
+            break;
+        }
+
+        if x >= horizontal_len {
+            // next line
+            x = 0;
+            y += 1;
+            continue;
+        }
+
+        let ch = matrix[y][x];
+        if ch == 'X' {
+            p1 += find_xmas(&matrix, x, y);
+        }
+
+        x += 1;
+    }
+
+    (p1, 0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn sample() {
+        let input = r#"MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX"#;
+
+        assert_eq!(solve(input), (18, 0));
+    }
+}

advent-of-code-2024/src/main.rs

@@ -1,6 +1,7 @@
 mod day01;
 mod day02;
 mod day03;
+mod day04;
 mod memory;
 
 fn main() {
@@ -30,4 +31,11 @@ fn main() {
     println!("  Part 2: {p2}");
 
     memory::print("after day03");
+
+    let (p1, p2) = day04::solve(include_str!("./testdata/day04"));
+    println!("Day 04");
+    println!("  Part 1: {p1}");
+    println!("  Part 2: {p2}");
+
+    memory::print("after day04");
 }