From 0750f8732e39c0aa21e8829df75cda52062bf9bf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20B=C3=BChler?= <stbuehler@web.de>
Date: Tue, 22 Dec 2020 09:40:19 +0100
Subject: [PATCH] day 22

---
 data/day22/input | 53 ++++++++++++++++++++++++++
 src/bin/day22.rs | 98 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 151 insertions(+)
 create mode 100644 data/day22/input
 create mode 100644 src/bin/day22.rs

diff --git a/data/day22/input b/data/day22/input
new file mode 100644
index 0000000..6b5d6d5
--- /dev/null
+++ b/data/day22/input
@@ -0,0 +1,53 @@
+Player 1:
+26
+8
+2
+17
+19
+29
+41
+7
+25
+33
+50
+16
+36
+37
+32
+4
+46
+12
+21
+48
+11
+6
+13
+23
+9
+
+Player 2:
+27
+47
+15
+45
+10
+14
+3
+44
+31
+39
+42
+5
+49
+24
+22
+20
+30
+1
+35
+38
+18
+43
+28
+40
+34
diff --git a/src/bin/day22.rs b/src/bin/day22.rs
new file mode 100644
index 0000000..efa7a01
--- /dev/null
+++ b/src/bin/day22.rs
@@ -0,0 +1,98 @@
+use std::collections::{VecDeque, HashSet};
+
+type Deck = VecDeque<u32>;
+
+const INPUT: &str = include_str!("../../data/day22/input");
+
+fn parse_player(block: &str) -> (u32, Deck) {
+    let block = block.strip_prefix("Player ").unwrap();
+    let player = block[..1].parse::<u32>().unwrap();
+    let block = block[1..].strip_prefix(":").unwrap().trim();
+    let deck = block.lines().map(|s| s.parse::<u32>().unwrap()).collect();
+    (player, deck)
+}
+
+fn score(deck: &Deck) -> u64 {
+    deck.iter().rev().enumerate().map(|(pos, &value)| {
+        ((pos + 1) as u64) * (value as u64)
+    }).sum::<u64>()
+}
+
+fn crab(mut deck1: Deck, mut deck2: Deck) {
+    while !deck1.is_empty() && !deck2.is_empty() {
+        let c1 = deck1.pop_front().unwrap();
+        let c2 = deck2.pop_front().unwrap();
+        if c1 > c2 {
+            deck1.push_back(c1);
+            deck1.push_back(c2);
+        } else {
+            assert!(c2 > c1);
+            deck2.push_back(c2);
+            deck2.push_back(c1);
+        }
+    }
+    if deck2.is_empty() {
+        println!("Player 1 won: {:?}", deck1);
+        println!("Score: {}", score(&deck1));
+    } else {
+        println!("Player 2 won: {:?}", deck2);
+        println!("Score: {}", score(&deck2));
+    }
+}
+
+fn _crab_rec(deck1: &mut Deck, deck2: &mut Deck) -> bool {
+    // println!("Rec Combat: {:?}, {:?}", deck1, deck2);
+    let mut previous_rounds = HashSet::new();
+    while !deck1.is_empty() && !deck2.is_empty() {
+        if !previous_rounds.insert((deck1.clone(), deck2.clone())) {
+            // prevent infinite loop; player 1 wins
+            return true;
+        }
+        let c1 = deck1.pop_front().unwrap();
+        let c2 = deck2.pop_front().unwrap();
+        let p1_won = if deck1.len() >= c1 as usize && deck2.len() >= c2 as usize {
+            let mut deck1: Deck = deck1.iter().copied().take(c1 as usize).collect();
+            let mut deck2: Deck = deck2.iter().copied().take(c2 as usize).collect();
+            assert_eq!(deck1.len(), c1 as usize);
+            assert_eq!(deck2.len(), c2 as usize);
+            // recurse
+            _crab_rec(&mut deck1, &mut deck2)
+        } else {
+            assert_ne!(c1, c2);
+            c1 > c2
+        };
+        if p1_won {
+            deck1.push_back(c1);
+            deck1.push_back(c2);
+        } else {
+            deck2.push_back(c2);
+            deck2.push_back(c1);
+        }
+    }
+    deck2.is_empty()
+}
+
+fn crab_rec(mut deck1: Deck, mut deck2: Deck) {
+    let p1_won = _crab_rec(&mut deck1, &mut deck2);
+    if p1_won {
+        println!("Player 1 won recursive combat: {:?}", deck1);
+        println!("Score: {}", score(&deck1));
+    } else {
+        println!("Player 2 won recursive combat: {:?}", deck2);
+        println!("Score: {}", score(&deck2));
+    }
+}
+
+fn main() {
+    let (deck1, deck2) = {
+        let pos = INPUT.find("\n\n").unwrap();
+        let (id1, deck1) = parse_player(&INPUT[..pos]);
+        let (id2, deck2) = parse_player(&INPUT[pos+2..]);
+        assert_eq!(id1, 1);
+        assert_eq!(id2, 2);
+        (deck1, deck2)
+    };
+
+    crab(deck1.clone(), deck2.clone());
+    crab_rec(deck1, deck2);
+}