Added older advents

advent_of_code_2018/day9/main2.cc

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+#include <iomanip>
+#include <iostream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+/*
+    $ time ./a.out < input.in 
+    Num players: 468
+    Last marble: 7184300
+    Highest reached score: 3156297594
+    ./a.out < input.in  0.16s user 0.05s system 99% cpu 0.203 total
+
+*/
+
+struct Game
+{
+    size_t num_players;
+    size_t last_marble;
+};
+
+istream &operator>>(istream &in, Game &game)
+{
+    cin >> game.num_players;
+    cin.ignore(31); // ignore ' players; last marble is worth '.
+    cin >> game.last_marble;
+    cin.ignore(8); // ignore '  points\n'
+
+    return in;
+}
+
+struct List
+{
+    size_t marble;
+    List *next;
+    List *previous;
+
+    List(size_t num)
+    : marble(num), next(this), previous(this)
+    { }
+
+    List *rotate(int direction)
+    {
+        List *rval = this;
+
+        if (direction > 0)
+        {
+            for (; direction--; )
+                rval = rval->next;
+        }
+        else 
+        {
+            direction *= -1;
+            for (; direction--; )
+                rval = rval->previous;
+        }
+
+        return rval;
+    }
+
+    List* insert_after(List *entry) //assume single entry
+    {
+        entry->next = next;
+        entry->next->previous = entry; 
+        entry->previous = this;
+        next = entry;
+
+        return entry;
+    }
+
+    //returns next in list. or nullptr when list size == 1
+    List* remove_current()
+    {
+        if (next == this)
+        {
+            delete this;
+            return nullptr;
+        }
+
+        next->previous = previous;
+        previous->next = next;
+
+        List *rval = next;
+        delete this;
+        return rval;
+    }
+
+    void print_list()
+    {
+        List *current = next;
+        cout << setw(5) << marble;
+
+        while (current != this)
+        {
+            cout << setw(5) << current->marble;
+            current = current->next;
+        }
+    }
+};
+
+int main()
+{
+
+    Game game;
+    cin >> game;
+
+    cout << "Num players: " << game.num_players << "\n";
+    cout << "Last marble: " << game.last_marble << "\n";
+
+    List *root = new List(0);
+    List *main = root;
+
+    vector<size_t> players;
+    players.resize(game.num_players, 0);
+
+    for (size_t idx = 1; idx < game.last_marble + 1; ++idx)
+    {
+        if (idx % 23 == 0)
+        {
+            size_t player = (idx + 1) % game.num_players;
+            players[player] += idx;
+
+            main = main->rotate(-7); //?
+            players[player] += main->marble;
+            main = main->remove_current();
+        }
+        else
+        {
+            main = main->rotate(1)->insert_after(new List(idx));
+        }
+    }
+
+    size_t player = 0;
+    for (size_t idx = 0; idx < game.num_players; ++idx)
+    {
+        if (players[player] < players[idx])
+            player = idx;
+    }
+
+    cout << "Highest reached score: " << players[player] << "\n";
+
+    while(root)
+        root = root->remove_current();
+
+}