aocpp/2020/18.cpp

#include <algorithm>
#include <cctype>
#include <cstdint>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <map>
#include <tuple>
#include <vector>

#include <doctest.h>

#include <aocpp/Startup.hpp>

namespace {

auto Eval(
  std::string const& input,
  std::map<char, std::pair<int, std::function<std::int64_t(std::int64_t,std::int64_t)>>> cfg
) -> std::int64_t
{
  std::vector<char> ops;
  std::vector<std::int64_t> vals;
  
  auto const eval1 = [&](){
    if (ops.size() < 1 || vals.size() < 2) {
      throw std::runtime_error{"parse error"};
    }
    if (auto opit = cfg.find(ops.back()); opit != cfg.end()) {
      std::int64_t y = vals.back(); vals.pop_back();
      std::int64_t x = vals.back(); vals.pop_back();
      vals.push_back(opit->second.second(x,y));
      ops.pop_back();
    } else {
      throw std::runtime_error{"parse error"};
    }
  };

  bool expect_operator = false;

  auto it = input.begin();
  while (it != input.end()) {
    char const c = *it++;

    // skip whitespace
    if (c == ' ') continue;

    // number literal
    if (std::isdigit(c)) {
      if (expect_operator) { throw std::runtime_error{"unexpected literal"}; }
      expect_operator = true;

      std::int64_t acc = c - '0';
      while (it != input.end() && std::isdigit(*it)) {
        acc = acc*10 + (*it++ - '0');
      }
      vals.push_back(acc);
      continue;
    }
    
    // begin subexpression
    if ('(' == c) {
      if (expect_operator) { throw std::runtime_error{"unexpected '('"}; }
      ops.push_back('(');
      continue;
    }
    
    // end subexpression
    if (')' == c) {
      if (!expect_operator) { throw std::runtime_error{"unexpected ')'"}; }
      while (!ops.empty() && ops.back() != '(') eval1();
      if (ops.empty()) throw std::runtime_error{"parse error"};
      ops.pop_back(); // '('
      continue;
    }
    
    // binary operator
    if (auto opit = cfg.find(c); opit != cfg.end()) {
      if (!expect_operator) { throw std::runtime_error{"unexpected operator"}; }
      expect_operator = false;
      while (!ops.empty() && cfg[ops.back()].first >= opit->second.first) eval1();
      ops.push_back(c);
      continue;
    }

    throw std::runtime_error{"unknown character"};
  }

  while (!ops.empty()) eval1();

  if (vals.empty()) { throw std::runtime_error{"empty input"}; }

  return vals.back();
}

auto Part1(std::string const& line) {
  return Eval(line, {{'+', {1, std::plus<std::int64_t>()}},{'*', {1, std::multiplies<std::int64_t>()}}});
}

auto Part2(std::string const& line) {
  return Eval(line, {{'+', {2, std::plus<std::int64_t>()}},{'*', {1, std::multiplies<std::int64_t>()}}});
}

} // namespace

TEST_SUITE("documented examples") {

TEST_CASE("part 1") {
  CHECK(Part1("1 + 2 * 3 + 4 * 5 + 6") == 71);
  CHECK(Part1("1 + (2 * 3) + (4 * (5 + 6))") == 51);
  CHECK(Part1("2 * 3 + (4 * 5)") == 26);
  CHECK(Part1("5 + (8 * 3 + 9 + 3 * 4 * 3)") == 437);
  CHECK(Part1("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))") == 12240);
  CHECK(Part1("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2") == 13632);
}

TEST_CASE("part 2") {
  CHECK(Part2("1 + 2 * 3 + 4 * 5 + 6") == 231);
  CHECK(Part2("1 + (2 * 3) + (4 * (5 + 6))") == 51);
  CHECK(Part2("2 * 3 + (4 * 5)") == 46);
  CHECK(Part2("5 + (8 * 3 + 9 + 3 * 4 * 3)") == 1445);
  CHECK(Part2("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))") == 669060);
  CHECK(Part2("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2") == 23340);
}

TEST_CASE("errors") {
  CHECK_THROWS_AS(Part1(""), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 + ()"), std::runtime_error);
  CHECK_THROWS_AS(Part1("(1"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 (2)"), std::runtime_error);
  CHECK_THROWS_AS(Part1(")"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1)"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 2"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 +"), std::runtime_error);
  CHECK_THROWS_AS(Part1("+ 1"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 /"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 / 2"), std::runtime_error);
  CHECK_THROWS_AS(Part1("1 + * 2"), std::runtime_error);
}

}

auto Main(std::istream & in, std::ostream & out) -> void
{
  std::int64_t part1 = 0;
  std::int64_t part2 = 0;
  
  std::string line;
  while (std::getline(in, line)) {
    part1 += Part1(line);
    part2 += Part2(line);
  }
  
  out << "Part 1: " << part1 << std::endl;
  out << "Part 2: " << part2 << std::endl;
}