day09 part 2

src/main.rs

@@ -1,4 +1,4 @@
 fn main() {
-    aoc_2018::tasks::day08::both();
-    // aoc_2018::tasks::day08::task2();
+    // aoc_2018::tasks::day09::task1();
+    aoc_2018::tasks::day09::task2();
 }

src/tasks/day09.rs

@@ -0,0 +1,94 @@
+const PLAYERS: usize = 468;
+const MODULO: usize = 23;
+const HIGHEST_MARBLE: usize = 7184300;
+
+pub fn task1() {
+    let mut player_score = [0usize; PLAYERS];
+    let mut current_player = 1;
+    let mut current_index: usize = 0;
+    let mut deck: Vec<usize> = Vec::new();
+    deck.push(0);
+    for marble in 1..=HIGHEST_MARBLE {
+        if marble % MODULO == 0 {
+            current_index = rem(current_index, 7, deck.len());
+            player_score[current_player] += marble;
+            player_score[current_player] += deck.remove(current_index);
+        } else {
+            current_index = (current_index + 2) % deck.len();
+            deck.insert(current_index, marble);
+        }
+        current_player = (current_player + 1) % PLAYERS;
+        if marble % 10000 == 0 {
+            println!("{} ({}%)", marble, marble as f32 / HIGHEST_MARBLE as f32);
+        }
+    }
+
+    let result = player_score.iter().max().unwrap();
+    println!("The highest score is {}", result);
+}
+
+pub fn rem(a: usize, sub: usize, m: usize) -> usize {
+    if sub > a {
+        (a + m - sub) % m
+    } else {
+        (a - sub) % m
+    }
+}
+
+pub fn task2() {
+    let _dummy_node = ListNode {
+        value: 0,
+        id_left: 0,
+        id_right: 0,
+    };
+
+    let mut player_score = [0usize; PLAYERS];
+    let mut current_player = 1;
+
+    let mut nodes = Vec::with_capacity(HIGHEST_MARBLE);
+    nodes.push(ListNode {
+        value: 0,
+        id_left: 0,
+        id_right: 0,
+    });
+    let mut current_node = &nodes[0];
+
+    for marble in 1..=HIGHEST_MARBLE {
+        if marble % MODULO == 0 {
+            for _ in 0..7 {
+                current_node = &nodes[current_node.id_left];
+            }
+            player_score[current_player] += marble;
+            player_score[current_player] += current_node.value;
+            let id_left = current_node.id_left;
+            let id_right = current_node.id_right;
+            nodes[id_left].id_right = id_right;
+            nodes[id_right].id_left = id_left;
+            current_node = &nodes[id_right];
+        } else {
+            let id_left = current_node.id_right;
+            let id_right = nodes[current_node.id_right].id_right;
+            let new = ListNode {
+                value: marble,
+                id_left,
+                id_right,
+            };
+            nodes.push(new);
+            let id_new = nodes.len() - 1;
+            nodes[id_left].id_right = id_new;
+            nodes[id_right].id_left = id_new;
+            current_node = &nodes[id_new];
+        }
+        current_player = (current_player + 1) % PLAYERS;
+    }
+
+    let result = player_score.iter().max().unwrap();
+    println!("The highest score is {}", result);
+}
+
+#[derive(Debug)]
+struct ListNode {
+    value: usize,
+    id_left: usize,
+    id_right: usize,
+}

src/tasks/mod.rs

@@ -6,3 +6,4 @@ pub mod day05;
 pub mod day06;
 pub mod day07;
 pub mod day08;
+pub mod day09;