Day4 task1 finished

Cargo.lock

@@ -21,6 +21,10 @@ dependencies = [
  "nom",
 ]
 
+[[package]]
+name = "day4"
+version = "0.1.0"
+
 [[package]]
 name = "memchr"
 version = "2.7.4"

day4/Cargo.toml

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

day4/src/common.rs

@@ -0,0 +1,18 @@
+pub(crate) type Matrix = Vec<Vec<char>>;
+
+pub(crate) fn parse_input(input: &str) -> Matrix {
+    parse_lines(input)
+        .into_iter()
+        .map(ToString::to_string)
+        .map(parse_line)
+        .filter(|array| !array.is_empty())
+        .collect()
+}
+
+pub(crate) fn parse_lines(input: &str) -> Vec<&str> {
+    input.split("\n").collect()
+}
+
+pub(crate) fn parse_line(line: String) -> Vec<char> {
+    line.trim().chars().collect()
+}

day4/src/input.txt

@@ -0,0 +1,140 @@
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day4/src/main.rs

@@ -0,0 +1,8 @@
+use crate::task1::task1;
+
+mod task1;
+mod common;
+
+fn main() {
+    task1();
+}

day4/src/task1.rs

@@ -0,0 +1,328 @@
+use crate::common::{parse_input, Matrix};
+use std::ops::{Add, Sub};
+
+pub(crate) fn task1() {
+    let raw_input = include_str!("./input.txt");
+    let matrix = parse_input(raw_input);
+    let occurrences = find_occurrences_of_xmas(matrix);
+
+    println!("The answer to task1 is {occurrences}");
+}
+
+const XMAS: [char; 4] = ['X', 'M', 'A', 'S'];
+
+fn find_occurrences_of_xmas(matrix: Matrix) -> usize {
+    matrix
+        .iter()
+        .enumerate()
+        .map(|(row_index, row)| {
+            row.iter()
+                .enumerate()
+                .filter(|(_, value)| **value == 'X')
+                .map(|(column_index, _)| count_from_position(&matrix, row_index, column_index))
+                .sum::<usize>()
+        })
+        .sum()
+}
+
+fn count_from_position(matrix: &Matrix, row_index: usize, column_index: usize) -> usize {
+    let row = &matrix[row_index];
+    [
+        look_up(matrix, row_index, column_index, &XMAS),
+        look_right_up(matrix, row_index, column_index, &XMAS),
+        look_right(row, column_index, &XMAS),
+        look_right_down(matrix, row_index, column_index, &XMAS),
+        look_down(matrix, row_index, column_index, &XMAS),
+        look_left_down(matrix, row_index, column_index, &XMAS),
+        look_left(row, column_index, &XMAS),
+        look_left_up(matrix, row_index, column_index, &XMAS),
+    ]
+    .iter()
+    .filter(|is_valid| **is_valid)
+    .count()
+}
+
+fn look_right(row: &[char], current_index: usize, keyword: &[char]) -> bool {
+    keyword.is_empty()
+        || keyword_matches_next_char_in_row(row, current_index, keyword)
+            && look_right(row, current_index + 1, &keyword[1..])
+}
+
+fn look_left(row: &[char], current_index: usize, keyword: &[char]) -> bool {
+    if keyword.is_empty() {
+        return true;
+    }
+    if keyword_matches_next_char_in_row(row, current_index, keyword) {
+        return if current_index > 0 {
+            look_left(row, current_index - 1, &keyword[1..])
+        } else {
+            keyword[1..].is_empty()
+        };
+    }
+    false
+}
+
+fn look_down(matrix: &Matrix, row_index: usize, column_index: usize, keyword: &[char]) -> bool {
+    look(
+        matrix,
+        row_index,
+        column_index,
+        keyword,
+        usize::add,
+        |value, _| value,
+        |_, _| true,
+    )
+}
+
+fn look_up(matrix: &Matrix, row_index: usize, column_index: usize, keyword: &[char]) -> bool {
+    look(
+        matrix,
+        row_index,
+        column_index,
+        keyword,
+        usize::sub,
+        |value, _| value,
+        |row_index, _| row_index > 0,
+    )
+}
+
+fn look_right_down(
+    matrix: &Matrix,
+    row_index: usize,
+    column_index: usize,
+    keyword: &[char],
+) -> bool {
+    look(
+        matrix,
+        row_index,
+        column_index,
+        keyword,
+        usize::add,
+        usize::add,
+        |_, _| true,
+    )
+}
+
+fn look_right_up(matrix: &Matrix, row_index: usize, column_index: usize, keyword: &[char]) -> bool {
+    look(
+        matrix,
+        row_index,
+        column_index,
+        keyword,
+        usize::sub,
+        usize::add,
+        |row_index, _| row_index > 0,
+    )
+}
+
+fn look_left_down(
+    matrix: &Matrix,
+    row_index: usize,
+    column_index: usize,
+    keyword: &[char],
+) -> bool {
+    look(
+        matrix,
+        row_index,
+        column_index,
+        keyword,
+        usize::add,
+        usize::sub,
+        |_, column_index| column_index > 0,
+    )
+}
+
+fn look_left_up(matrix: &Matrix, row_index: usize, column_index: usize, keyword: &[char]) -> bool {
+    look(
+        matrix,
+        row_index,
+        column_index,
+        keyword,
+        usize::sub,
+        usize::sub,
+        |row_index, column_index| row_index > 0 && column_index > 0,
+    )
+}
+
+fn look(
+    matrix: &Matrix,
+    row_index: usize,
+    column_index: usize,
+    keyword: &[char],
+    row_op: fn(usize, usize) -> usize,
+    column_op: fn(usize, usize) -> usize,
+    guard: fn(row_index: usize, column_index: usize) -> bool,
+) -> bool {
+    if keyword.is_empty() {
+        return true;
+    }
+    if keyword_matches_next_char_in_column(matrix, row_index, column_index, keyword) {
+        return if guard(row_index, column_index) {
+            look(
+                matrix,
+                row_op(row_index, 1),
+                column_op(column_index, 1),
+                &keyword[1..],
+                row_op,
+                column_op,
+                guard,
+            )
+        } else {
+            keyword[1..].is_empty()
+        };
+    }
+    false
+}
+
+fn keyword_matches_next_char_in_column(
+    matrix: &Matrix,
+    row_index: usize,
+    column_index: usize,
+    keyword: &[char],
+) -> bool {
+    matrix
+        .get(row_index)
+        .and_then(|row| row.get(column_index))
+        .and_then(|character| keyword.first().map(|first_char| *character == *first_char))
+        .take_if(|matches| *matches)
+        .is_some()
+}
+
+fn keyword_matches_next_char_in_row(row: &[char], current_index: usize, keyword: &[char]) -> bool {
+    row.get(current_index)
+        .and_then(|character| keyword.first().map(|first_char| *character == *first_char))
+        .take_if(|matches| *matches)
+        .is_some()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::common::{parse_input, parse_line};
+    use crate::task1::{
+        find_occurrences_of_xmas, look_down, look_left, look_left_up, look_right, look_right_up,
+        look_up, XMAS,
+    };
+
+    #[test]
+    fn test_look_right() {
+        let input = String::from("MMMSXXMASM");
+        let row = parse_line(input);
+        assert!(look_right(&row, 5, &XMAS))
+    }
+
+    #[test]
+    fn test_look_right_invalid() {
+        let input = String::from("MMMSXXMASM");
+        let row = parse_line(input);
+        assert!(!look_right(&row, 0, &XMAS))
+    }
+
+    #[test]
+    fn test_look_left() {
+        let input = String::from("MSAMXMSMSA");
+        let row = parse_line(input);
+        assert!(look_left(&row, 4, &XMAS))
+    }
+
+    #[test]
+    fn test_look_down() {
+        let input = r#"
+        M
+        A
+        M
+        X
+        M
+        A
+        S
+        A
+        M
+        X
+        "#;
+        let matrix = parse_input(input);
+        assert!(look_down(&matrix, 3, 0, &XMAS))
+    }
+
+    #[test]
+    fn test_look_up() {
+        let input = r#"
+        M
+        S
+        A
+        M
+        X
+        X
+        S
+        S
+        M
+        M
+        "#;
+        let matrix = parse_input(input);
+        assert!(look_up(&matrix, 4, 0, &['X', 'M', 'A', 'S']))
+    }
+
+    #[test]
+    fn test_look_right_up() {
+        let input = r#"
+        MSMS
+        AXAM
+        AMMM
+        XMXA
+        "#;
+        let matrix = parse_input(input);
+        assert!(look_right_up(&matrix, 3, 0, &XMAS));
+    }
+
+    #[test]
+    fn test_look_left_up() {
+        let input = r#"
+        SMSM
+        MAXA
+        MAMM
+        MXMX
+        "#;
+        let matrix = parse_input(input);
+        assert!(look_left_up(&matrix, 3, 3, &XMAS));
+    }
+
+    #[test]
+    fn test_look_left_up_and_right_up() {
+        let input = r#"
+        SMSMSAS
+        SAXAMAS
+        MAMMMXM
+        MXMXAXM
+        "#;
+        let matrix = parse_input(input);
+        assert_eq!(4, find_occurrences_of_xmas(matrix))
+    }
+
+    #[test]
+    fn test_multiple_directions() {
+        let input = r#"
+        SMSMSASXSS
+        SAXAMASAAA
+        MAMMMXMMMM
+        MXMXAXMASX
+        "#;
+        let matrix = parse_input(input);
+        assert_eq!(8, find_occurrences_of_xmas(matrix))
+    }
+
+    #[test]
+    fn test_task1() {
+        let input = r#"
+        MMMSXXMASM
+        MSAMXMSMSA
+        AMXSXMAAMM
+        MSAMASMSMX
+        XMASAMXAMM
+        XXAMMXXAMA
+        SMSMSASXSS
+        SAXAMASAAA
+        MAMMMXMMMM
+        MXMXAXMASX
+        "#;
+        let matrix = parse_input(input);
+        assert_eq!(18, find_occurrences_of_xmas(matrix))
+    }
+}