day2: problem 2 solution

2/src/main.rs

@@ -165,6 +165,51 @@ fn problem1(input: InputIter) -> u64 {
 }
 
 // PROBLEM 2 solution
-fn problem2(input: InputIter) -> u64 {
+
-    0
+// --- Part Two ---
+
+// The Elf says they've stopped producing snow because they aren't getting any water! He
+// isn't sure why the water stopped; however, he can show you how to get to the water
+// source to check it out for yourself. It's just up ahead!
+
+// As you continue your walk, the Elf poses a second question: in each game you played,
+// what is the fewest number of cubes of each color that could have been in the bag to
+// make the game possible?
+
+// Again consider the example games from earlier:
+
+// 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
+
+//     In game 1, the game could have been played with as few as 4 red, 2 green, and 6
+//     blue cubes. If any color had even one fewer cube, the game would have been
+//     impossible. Game 2 could have been played with a minimum of 1 red, 3 green, and 4
+//     blue cubes. Game 3 must have been played with at least 20 red, 13 green, and 6
+//     blue cubes. Game 4 required at least 14 red, 3 green, and 15 blue cubes. Game 5
+//     needed no fewer than 6 red, 3 green, and 2 blue cubes in the bag.
+
+// The power of a set of cubes is equal to the numbers of red, green, and blue cubes
+// multiplied together. The power of the minimum set of cubes in game 1 is 48. In games
+// 2-5 it was 12, 1560, 630, and 36, respectively. Adding up these five powers produces
+// the sum 2286.
+
+// For each game, find the minimum set of cubes that must have been present. What is the
+// sum of the power of these sets?
+
+
+// Minimum power = maximum seen of each colour across all games, r * g * b
+fn problem2_game_minimum_power(game: &GameResult) -> u64 {
+    // Could be done in one pass, but this is cleaner using Iter methods
+    let max_r = game.results.iter().map(|c| c.red).max().unwrap();
+    let max_g = game.results.iter().map(|c| c.green).max().unwrap();
+    let max_b = game.results.iter().map(|c| c.blue).max().unwrap();
+
+    max_r * max_g * max_b
+}
+
+fn problem2(input: InputIter) -> u64 {
+    let games = input.map(|l| GameResult::from(l.unwrap().as_str()));
+    games.fold(0u64, |accum, val| accum + problem2_game_minimum_power(&val))
 }