Dartで第3回オフラインリアルタイムどう書く

第3回オフラインリアルタイムどう書くの問題をDartで解いてみました。

import "dart:collection";

main() {
  test("b", "AB");
  test("l", "AD");
  test("r", "AC");
  test("bbb", "ABAB");
  test("rrr", "ACBA");
  test("blll", "ABCAB");
  test("llll", "ADEBA");
  test("rbrl", "ACADE");
  test("brrrr", "ABEDAB");
  test("llrrr", "ADEFDE");
  test("lrlll", "ADFEDF");
  test("lrrrr", "ADFCAD");
  test("rllll", "ACFDAC");
  test("blrrrr", "ABCFEBC");
  test("brllll", "ABEFCBE");
  test("bbrllrrr", "ABACFDEFD");
  test("rrrrblll", "ACBACABCA");
  test("llrlrrbrb", "ADEFCADABA");
  test("rrrbrllrr", "ACBABEFCAD");
  test("llrllblrll", "ADEFCBCADEB");
  test("lrrlllrbrl", "ADFCBEFDFCB");
  test("lllrbrrlbrl", "ADEBCBACFCAB");
  test("rrrrrrlrbrl", "ACBACBADFDEB");
  test("lbrbbrbrbbrr", "ADABABEBCBCFE");
  test("rrrrlbrblllr", "ACBACFCACFDAB");
  test("lbbrblrlrlbll", "ADADFDABCFDFED");
  test("rrbbrlrlrblrl", "ACBCBADFEBEFDA");
  test("blrllblbrrrrll", "ABCFDADEDABEDFE");
  test("blrllrlbllrrbr", "ABCFDABCBEFDEDA");
  test("lbrbbrllllrblrr", "ADABABEFCBEDEBCF");
  test("rrrrbllrlrbrbrr", "ACBACABCFDEDADFC");
  print("ok");
}

test(String input, String expect) {
  var q = new ListQueue.from(input.split(""));
  assert(walk(q, "B", "A") == expect);
}

final graph = {
  "A": "BCD",
  "B": "CAE",
  "C": "ABF",
  "D": "EAF",
  "E": "FBD",
  "F": "CED",
};

String walk(Queue input, String from, String to) {
  if(input.isEmpty) return to;

  String direction = input.removeFirst();
  if(direction == "b") return to.concat(walk(input, to, from));

  String nexts = graph[to].concat(graph[to]);
  int i = nexts.indexOf(from);
  String lr = nexts.slice(i + 1, i + 3);
  return to.concat(walk(input, to, lr[direction == "l" ? 1 : 0]));
}