Solutions for day14, day18, day19

2016/day19/Cargo.lock

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+[root]
+name = "day19"
+version = "0.1.0"
+

2016/day19/Cargo.toml

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+[package]
+name = "day19"
+version = "0.1.0"
+authors = ["~krowbar"]
+
+[dependencies]

2016/day19/src/main.rs

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+// First game
+// 1 1 -> 2 0
+// 1 1 1 1 -> 2 0 2 0 -> 4 0 0 0 //first
+// 1 1 1 1 1 1 -> 2 0 2 0 2 0 -> 0 0 0 0 6 0
+
+// 1 -> 1
+// 1 1 1                 -> 0 0 3 //last player
+// 1 1 1 1 1             -> 0 0 2 0 3             -> 0 0 5 0 0 //middle player
+// 1 1 1 1 1 1 1         -> 0 0 2 0 2 0 3         -> 0 0 0 0 0 0 7 //last player
+// 1 1 1 1 1 1 1 1 1     -> 0 0 2 0 2 0 2 0 3     -> 0 0 4 0 0 0 5 0 0 -> 0 0 9 0 0 0 0 0 0 //third player
+// 1 1 1 1 1 1 1 1 1 1 1 -> 0 0 2 0 2 0 2 0 2 0 3 -> 0 0 0 0 0 0 4 0 0 0 7 -> 0 0 0 0 0 0 11 0 0 0 0 //7th player
+
+// generate list
+//   filter based on size
+//     filter_even: keep all with even idx
+//     filter_odd: keep all with even idx except 0
+//   repeat until one remains
+
+fn pass_gifts(players: Vec<i64>) -> i64 {
+    //represents the group of players left after a pass
+    let is_odd = players.len() % 2 == 1;
+    let new_players = players.iter().enumerate().filter(|e| !(is_odd && e.0 == 0) && e.0 % 2 == 0).map(|e| *e.1).collect::<Vec<_>>();
+    //println!("{:?}", new_players);
+    if new_players.len() == 1 {
+        new_players[0]
+    } else {
+        pass_gifts(new_players)
+    }
+}
+
+fn play_game(size: i64) -> i64 {
+    //take the size of the group and returns the winner
+    let players: Vec<i64> = (1..size+1).collect();
+    //println!("{:?}", players);
+    pass_gifts(players)
+}
+
+
+// Second game
+// 1 2 3 4     -> 1 2 - 4   -> 1 2 - -   -> 1
+// 1 2 3 4 5   -> 1 2 - 4 5 -> 1 2 - 4 - -> - 2 - 4 - -> 2
+// 1 2 3 4 5 6 ->
+//looping though all players, remove player at position  floor(players.len()/2) + player_idx
+
+fn play_new_game(size: i64) -> i64 {
+    let mut players = (1..size+1).collect::<Vec<i64>>();
+    println!("Set up vector of {} players", size);
+    let mut current_player_idx = 0;
+    let mut player_idx_to_eliminate;
+    let mut player_len = size as usize;
+
+    while player_len > 1 {
+        player_idx_to_eliminate = (player_len/2 /*drops fraction*/ + current_player_idx) % player_len;
+        //println!("Removing idx {} from players (size {}) {:?}", player_idx_to_eliminate, players.len(), players);
+        //players.remove(player_idx_to_eliminate);
+        players = players.iter().enumerate().filter(|e| e.0 != player_idx_to_eliminate).map(|e| *e.1).collect::<Vec<_>>();
+        player_len = player_len - 1;
+
+        current_player_idx = current_player_idx + match player_idx_to_eliminate > current_player_idx {
+             true => 1,
+             false => 0
+        } % player_len;
+    }
+    //println!("Returning {:?}", players);
+    players[0]
+}
+
+fn main() {
+    let winner = play_game(3014387);
+    println!("Part 1: Winner is {}", winner);
+
+    //Need to improve the algorithm so it finishes in a sane amount of time
+    let new_winner = play_new_game(3014387);
+    println!("Part 2: Winner is {}", new_winner);
+}