Initial commit

2020/puzzle-22-02.cc

@@ -0,0 +1,129 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using Card = unsigned;
+using Cards = std::list<Card>;
+using Score = unsigned long;
+using Hash = std::string;
+
+struct Player {
+  Player(std::istream &is) {
+    std::string line;
+    if (!std::getline(is, name_)) {
+      assert(false);
+    }
+    while (std::getline(is, line)) {
+      if (line == "") {
+        break;
+      }
+      cards_.push_back(std::stoul(line));
+    }
+  }
+
+  bool empty() const { return cards_.empty(); }
+  Card front() const { return cards_.front(); }
+  void pop_front() { cards_.pop_front(); }
+  void push_back(Card c) { cards_.push_back(c); }
+  std::size_t size() const { return cards_.size(); }
+
+  Score score() const {
+    Score r = 0;
+    unsigned idx = 1;
+    for (auto it = cards_.rbegin(); it != cards_.rend(); ++it) {
+      r += idx * *it;
+      ++idx;
+    }
+    return r;
+  }
+
+  Hash hash() const {
+    std::string r = name_;
+    for (auto c : cards_) {
+      assert(c > 0);
+      assert(c < 128);
+      r += (char)c;
+    }
+
+    return r;
+  }
+
+  Player(Player const &prev, Card size) : name_(prev.name_ + "-") {
+    auto it = prev.cards_.begin();
+    for (Card i = 0; i < size; ++i) {
+      cards_.push_back(*it++);
+    }
+  }
+
+  friend std::ostream &operator<<(std::ostream &os, Player const &p);
+
+private:
+  std::string name_;
+  Cards cards_;
+};
+
+std::ostream &operator<<(std::ostream &os, Player const &p) {
+  os << p.name_;
+  for (auto c : p.cards_) {
+    os << " " << c;
+  }
+  return os;
+}
+
+// False = p1 wins, true = p2 wins.
+bool play_game(Player &p1, Player &p2) {
+  std::set<Hash> hashes;
+
+  while (!p1.empty() && !p2.empty()) {
+    // Ensure we've not seen this configuration before.
+    auto [it, success] = hashes.insert(p1.hash() + p2.hash());
+    if (!success) {
+      return false;
+    }
+
+    Card c1 = p1.front();
+    Card c2 = p2.front();
+    p1.pop_front();
+    p2.pop_front();
+    if (p1.size() >= c1 && p2.size() >= c2) {
+      Player sp1(p1, c1);
+      Player sp2(p2, c2);
+      bool result = play_game(sp1, sp2);
+      if (!result) {
+        p1.push_back(c1);
+        p1.push_back(c2);
+      } else {
+        p2.push_back(c2);
+        p2.push_back(c1);
+      }
+    } else if (c1 > c2) {
+      p1.push_back(c1);
+      p1.push_back(c2);
+    } else if (c1 < c2) {
+      p2.push_back(c2);
+      p2.push_back(c1);
+    } else {
+      assert(false);
+    }
+  }
+
+  return p1.empty();
+}
+
+int main(void) {
+  Player player1(std::cin);
+  Player player2(std::cin);
+
+  play_game(player1, player2);
+  Score final_score = player1.score() + player2.score();
+  std::cout << "Final score: " << final_score << "\n";
+  return 0;
+}