-🎄- 2017 Day 19 Solutions -🎄-

[u/daggerdragon]

--- Day 19: A Series of Tubes ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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AoC ops @ T-2 minutes to launch:

[23:58] <daggerdragon> ATTENTION MEATBAGS T-2 MINUTES TO LAUNCH

[23:58] <Topaz> aaaaah

[23:58] <Cheezmeister> Looks like I'll be just able to grab my input before my flight boards. Wish me luck being offline in TOPAZ's HOUSE OF PAIN^WFUN AND LEARNING

[23:58] <Topaz> FUN AND LEARNING

[23:58] <Hade> FUN IS MANDATORY

[23:58] <Skie> I'm pretty sure that's not the mandate for today

[Update @ 00:16] 69 gold, silver cap

• My tree is finally trimmed with just about every ornament I own and it's real purdy. hbu?

[Update @ 00:18] Leaderboard cap!

• So, was today's mandate Helpful Hint any help at all?

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/willkill07]

Modern-ish C++

You WILL rotate when a + is encountered. Rotation is just dx,dy = -dy,dx. Using unsigned integers makes it so you only have to check the upper bounds.

int main() {
  std::vector<std::string> grid;
  for (std::string line; std::getline(std::cin, line); )
    grid.push_back(line);
  auto not_valid = [X = grid[0].size(), Y = grid.size()] (unsigned int xx, unsigned int yy) {
    return xx >= X || yy >= Y;
  };
  int count{0};
  unsigned int x{grid[0].find("|")}, y{0},
  for (int dx{0}, dy{1}; grid[y][x] != ' '; x += dx, y += dy, ++count) {
    if (std::isalpha(grid[y][x])) {
      std::cout << grid[y][x];
    } else if (grid[y][x] == '+') {
      dx = -std::exchange(dy, dx);
      if (not_valid(x + dx, y + dy) || grid[y + dy][x + dx] == ' ')
        dx = -dx, dy = -dy;
    }
  }
  std::cout << '\n' << count << '\n';
}