import 'dart:math';
import 'eulib.dart';

void main() {
  var cards = List.generate(1000000, (index) => index + 1);
  var front = '418976235'.split('').map(int.parse).toList();
  cards.replaceRange(0, 9, front);
  var game = Game(cards);
  for (var _ in range(0, 10000000)) {
    game.playRound();
  }
  var c1 = game.succ[1];
  var c2 = game.succ[c1];
  assert(c1 * c2 == 563362809504);
}

class Game {
  List<int> succ;
  int currentValue;
  int lo, hi;

  Game(List<int> c) {
    lo = c.reduce(min);
    hi = c.reduce(max);
    succ = List.filled(hi + 1, 0);
    for (var i in range(0, c.length - 1)) {
      succ[c[i]] = c[i + 1];
    }
    succ[c.last] = c.first;

    currentValue = c.first;
  }

  void playRound() {
    // Pick the three after current.
    var rfirst = succ[currentValue];
    var rmid = succ[rfirst];
    var rlast = succ[rmid];
    var rem = [rfirst, rmid, rlast];

    // Extract them by joining the pred and succ.
    succ[currentValue] = succ[rlast];

    // Find destination value.
    var d = currentValue - 1;
    if (d < lo) d = hi;
    while (rem.contains(d)) {
      d -= 1;
      if (d < lo) d = hi;
    }
    // Insert cards there.
    succ[rlast] = succ[d];
    succ[d] = rfirst;
    // Update current.
    currentValue = succ[currentValue];
  }

  String endString() {
    var pos = 1;
    var ret = <int>[];
    while (succ[pos] != 1) {
      pos = succ[pos];
      ret.add(pos);
    }
    return ret.join('');
  }
}