Solve day 02, part one

data/examples/02.txt

@@ -0,0 +1,5 @@
+Game 1: 3 blue, 4 red; 1 red, 2 green, 6 blue; 2 green
+Game 2: 1 blue, 2 green; 3 green, 4 blue, 1 red; 1 green, 1 blue
+Game 3: 8 green, 6 blue, 20 red; 5 blue, 4 red, 13 green; 5 green, 1 red
+Game 4: 1 green, 3 red, 6 blue; 3 green, 6 red; 3 green, 15 blue, 14 red
+Game 5: 6 red, 1 blue, 3 green; 2 blue, 1 red, 2 green

src/bin/02.rs

@@ -0,0 +1,86 @@
+advent_of_code::solution!(2);
+
+use std::collections::HashMap;
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let max_cubes = HashMap::from([("red", 12), ("green", 13), ("blue", 14)]);
+
+    // Game ID
+    let mut index: u32 = 1;
+
+    input
+        .lines()
+        .map(|game| {
+            let mut possible_game = true; // assume that games are possible by default
+
+            // Extract sets from game
+            // - Referencing the string slice is faster than splitting with ": "
+            // - Ignoring the ID, 'Game ID: ' has 7 constant chars.
+            // - To calculate the ID length, we use log10: id_length = log10(index) + 1
+            let sets: &Vec<&str> = &game[(7 + index.checked_ilog10().unwrap_or(0) + 1)
+                .try_into()
+                .unwrap()..]
+                .split("; ")
+                .collect::<Vec<_>>();
+
+            // Determine if the game is possible for each set
+            for set in sets {
+                let cubes = set
+                    .split(", ")
+                    .map(|x| x.split(' ').collect::<Vec<_>>())
+                    .collect::<Vec<_>>();
+
+                // Compare examined cubes with maximum values
+                for cube in cubes.iter() {
+                    let color = cube[1];
+                    let number = cube[0].parse::<i32>().unwrap();
+                    let max_number = *max_cubes.get(color).unwrap();
+
+                    // If the game is impossible, skip the rest of the cubes
+                    if number > max_number {
+                        possible_game = false;
+                        break;
+                    }
+                }
+
+                // If the game is impossible, skip its unchecked sets
+                if possible_game == false {
+                    break;
+                }
+            }
+
+            // Move on to the next game
+            index += 1;
+
+            if possible_game == true {
+                // We need to remove 1 since index starts from 1, not 0
+                index - 1
+            } else {
+                0
+            }
+        })
+        .sum::<u32>()
+        .try_into()
+        .ok()
+}
+
+pub fn part_two(_input: &str) -> Option<u32> {
+    None
+}
+
+#[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, Some(8));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}