day 4

README.md

@@ -22,6 +22,7 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 1](./src/bin/01.rs) | `40.7µs` | `58.2µs` |
 | [Day 2](./src/bin/02.rs) | `117.1µs` | `205.3µs` |
 | [Day 3](./src/bin/03.rs) | `115.1µs` | `148.7µs` |
+| [Day 4](./src/bin/04.rs) | `81.9µs` | `51.3µs` |
 
-**Total: 0.69ms**
+**Total: 0.82ms**
 <!--- benchmarking table --->

data/examples/04.txt

@@ -0,0 +1,10 @@
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX

src/bin/04.rs

@@ -0,0 +1,238 @@
+use itertools::Itertools;
+
+advent_of_code::solution!(4);
+
+const XMAS: [char; 4] = ['X', 'M', 'A', 'S'];
+const MAS: [char; 3] = ['M', 'A', 'S'];
+const SAM: [char; 3] = ['S', 'A', 'M'];
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let matrix = input
+        .lines()
+        .map(|line| line.chars().collect_vec())
+        .collect_vec();
+
+    let y_range = matrix.len();
+    let x_range = matrix[0].len();
+
+    let mut found = 0;
+    for y in 0..y_range {
+        for x in 0..x_range {
+            if check_north(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_northeast(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_east(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_southeast(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_south(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_southwest(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_west(&matrix, x, y) {
+                found += 1;
+            };
+
+            if check_northwest(&matrix, x, y) {
+                found += 1;
+            };
+        }
+    }
+    Some(found)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let matrix = input
+        .lines()
+        .map(|line| line.chars().collect_vec())
+        .collect_vec();
+
+    let y_range = matrix.len();
+    let x_range = matrix[0].len();
+
+    let mut found = 0;
+    for y in 0..y_range {
+        for x in 0..x_range {
+            if check_x_mas(&matrix, x, y) {
+                found += 1;
+            };
+        }
+    }
+    Some(found)
+}
+
+fn check_north(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if y < 3 {
+        return false;
+    }
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test_col) = matrix.get(y - idx) {
+            if &to_test_col[x] != test_char {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_northeast(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if y < 3 {
+        return false;
+    }
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test_col) = matrix.get(y - idx) {
+            if let Some(to_test) = to_test_col.get(x + idx) {
+                if to_test != test_char {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_east(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test) = matrix[y].get(x + idx) {
+            if to_test != test_char {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_southeast(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test_col) = matrix.get(y + idx) {
+            if let Some(to_test) = to_test_col.get(x + idx) {
+                if to_test != test_char {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_south(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test_col) = matrix.get(y + idx) {
+            if &to_test_col[x] != test_char {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_southwest(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x < 3 {
+        return false;
+    }
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test_col) = matrix.get(y + idx) {
+            if let Some(to_test) = to_test_col.get(x - idx) {
+                if to_test != test_char {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_west(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x < 3 {
+        return false;
+    }
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test) = matrix[y].get(x - idx) {
+            if to_test != test_char {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_northwest(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x < 3 || y < 3 {
+        return false;
+    }
+    for (idx, test_char) in XMAS.iter().enumerate() {
+        if let Some(to_test_col) = matrix.get(y - idx) {
+            if let Some(to_test) = to_test_col.get(x - idx) {
+                if to_test != test_char {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+    true
+}
+
+fn check_x_mas(matrix: &[Vec<char>], x: usize, y: usize) -> bool {
+    if x < 1 || y < 1 || y > matrix.len() - 2 || x > matrix[0].len() - 2 {
+        return false;
+    }
+
+    let word1 = [matrix[y - 1][x - 1], matrix[y][x], matrix[y + 1][x + 1]];
+    let word2 = [matrix[y + 1][x - 1], matrix[y][x], matrix[y - 1][x + 1]];
+
+    (word1 == SAM || word1 == MAS) && (word2 == MAS || word2 == SAM)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}