Finished day 3 aoc, going smooth so far, fearing for the next days

advent_of_code/2023/3/src/main.rs

@@ -1,3 +1,4 @@
+use std::collections::HashSet;
 use std::fmt;
 
 #[derive(Debug, Clone, Copy, Default)]
@@ -119,6 +120,41 @@ fn get_positions_to_check(
     positions_to_check
 }
 
+fn get_gear_positions(engine: &Vec<Vec<Tile>>) -> Vec<(usize, usize)> {
+    let mut result = vec![];
+    for (row_number, row) in engine.iter().enumerate() {
+        for (column_number, tile) in row.iter().enumerate() {
+            match tile {
+                Tile::Symbol('*') => result.push((row_number, column_number)),
+                _ => {}
+            }
+        }
+    }
+
+    result
+}
+
+fn get_gear_ratio_number(engine: &Vec<Vec<Tile>>, starting_point: (usize, usize)) -> u64 {
+    let mut starting_column = starting_point.1;
+
+    while let Some(Tile::Digit(_)) = engine[starting_point.0].get(starting_column - 1) {
+        starting_column -= 1;
+        if starting_column == 0 {
+            break;
+        }
+    }
+
+    let mut result = 0;
+    let mut column = starting_column;
+
+    while let Some(Tile::Digit(d)) = engine[starting_point.0].get(column) {
+        result = result * 10 + d;
+        column += 1;
+    }
+
+    result
+}
+
 fn solve_1(engine: &Vec<Vec<Tile>>) -> u64 {
     let mut result = 0;
     let engine_width = engine[0].len();
@@ -144,6 +180,43 @@ fn solve_1(engine: &Vec<Vec<Tile>>) -> u64 {
     result
 }
 
+fn solve_2(engine: &Vec<Vec<Tile>>) -> u64 {
+    let mut result = 0;
+
+    let engine_width = engine[0].len();
+    let engine_height = engine.len();
+
+    let gears_to_check = get_gear_positions(&engine);
+
+    for (gear_x, gear_y) in gears_to_check {
+        let positions_to_check =
+            get_positions_to_check((gear_x, (gear_y, gear_y)), engine_width, engine_height);
+
+        let mut adjacent_engine_part_positions = HashSet::new();
+        for (x, y) in positions_to_check {
+            match engine[x][y] {
+                Tile::Digit(_) => {
+                    if !(adjacent_engine_part_positions.contains(&(x, y - 1))
+                        || adjacent_engine_part_positions.contains(&(x, y + 1)))
+                    {
+                        adjacent_engine_part_positions.insert((x, y));
+                    }
+                }
+                _ => {}
+            }
+        }
+
+        if adjacent_engine_part_positions.len() == 2 {
+            result += adjacent_engine_part_positions
+                .into_iter()
+                .map(|coord| get_gear_ratio_number(&engine, coord))
+                .product::<u64>();
+        }
+    }
+
+    result
+}
+
 fn main() {
     println!("Hello, this is Patrick!");
 
@@ -155,6 +228,11 @@ fn main() {
         "The sum of all the part numbers in the engine schematic is {}",
         solve_1(&engine)
     );
+
+    println!(
+        "The sum of all gear ratios in the engine schematic is {}",
+        solve_2(&engine)
+    );
 }
 
 #[cfg(test)]
@@ -169,4 +247,13 @@ mod tests {
 
         assert_eq!(solve_1(&engine), 4361);
     }
+
+    #[test]
+    fn test_2() {
+        let test_input = include_str!("../test_input.txt");
+
+        let engine = parse_input(test_input);
+
+        assert_eq!(solve_2(&engine), 467835);
+    }
 }