main.dart

bool hasDoubleDecker(values) {
  if (values == null || values.length < 5) {
    return false;
  }

  for (var i = 0; i < values.length - 4; i++) {
    if (values[i] == values[i + 2] &&
        values[i] == values[i + 4] &&
        values[i + 1] == values[i + 3]) {
      return true;
    }
  }

  return false;
}

bool cleanerHasDoubleDecker(values) {
  if (values == null || values.length < 5) {
    return false;
  }

  for (var i = 0; i < values.length - 4; i++) {
    if (values[i] == values[i + 2] &&
        values[i] == values[i + 4] &&
        values[i + 1] == values[i + 3]) {
      return true;
    } else {
      if (values[i] != values[i + 2]) {
        i++;
      } else if (values[i + 1] != values[i + 3]) {
        i += 2;
      } else if (values[i] != values[i + 4]) {
        i += 3;
      }
    }
  }
  
  return false;
}

int longestDoubleDecker(values) {
  if (values == null || values.length < 5) {
    return 0;
  }
  
  var longestDoubleDecker = 0;
  var currentDoubleDeckerCount = 0;
  for (var i = 0; i < values.length - 4; i++) {
    if (hasDoubleDecker(values.sublist(i, i + 5))) {
      currentDoubleDeckerCount++;
    
    if (currentDoubleDeckerCount > longestDoubleDecker) {
        longestDoubleDecker = currentDoubleDeckerCount;
    }
    } else {
      currentDoubleDeckerCount = 0;
    }
  }
  
  return longestDoubleDecker;
}

main() {
  print('hasDoubleDecker');
  print(hasDoubleDecker(null));
  print(hasDoubleDecker([0]));
  print(hasDoubleDecker([0, 1, 0, 1]));
  print(hasDoubleDecker([0, 1, 0, 1, 0]));
  print(hasDoubleDecker([0, 1, 0, 1, 0, 1]));
  print(hasDoubleDecker([0, 1, 0, 1, 2, 1]));
  print(hasDoubleDecker([0, 1, 2, 3, 2, 3, 2, 3, 1]));
  print(hasDoubleDecker([0, 1, 2, 3, 2, 3, 4, 5, 4, 5, 4]));
  
  print('');
  
  print('cleanerHasDoubleDecker');
  print(cleanerHasDoubleDecker(null));
  print(cleanerHasDoubleDecker([0]));
  print(cleanerHasDoubleDecker([0, 1, 0, 1]));
  print(cleanerHasDoubleDecker([0, 1, 0, 1, 0]));
  print(cleanerHasDoubleDecker([0, 1, 0, 1, 0, 1]));
  print(cleanerHasDoubleDecker([0, 1, 0, 1, 2, 1]));
  print(cleanerHasDoubleDecker([0, 1, 2, 3, 2, 3, 2, 3, 1]));
  print(cleanerHasDoubleDecker([0, 1, 2, 3, 2, 3, 4, 5, 4, 5, 4]));
  
  print('');
  
  print('longestDoubleDecker');
  print(longestDoubleDecker(null));
  print(longestDoubleDecker([0]));
  print(longestDoubleDecker([0, 1, 0, 1]));
  print(longestDoubleDecker([0, 1, 0, 1, 0]));
  print(longestDoubleDecker([0, 1, 0, 1, 0, 1]));
  print(longestDoubleDecker([0, 1, 0, 1, 0, 1, 2, 1, 0, 1, 0, 1]));
  print(longestDoubleDecker([0, 1, 0, 1, 0, 1, 2, 1, 0, 1, 0, 1, 2]));
  print(longestDoubleDecker([2, 0, 1, 0, 1, 0, 1, 2, 1, 0, 1, 0, 1, 2]));
}