aoc24/12/main.cc

#include <fstream>
#include <iostream>
#include <sstream>
#include <vector>
#include <tuple>
#include <set>

using namespace std;

#ifdef DEBUG
#define DBG(str) do { std::cout << str << std::endl; } while( false )
#else
#define DBG(str) do { } while ( false )
#endif

vector<vector<char>> parseGrid(const char *path) {
  vector<vector<char>> grid;

  ifstream input(path);
  string line;
  while (getline(input, line)) {
    char c;
    vector<char> row;
    stringstream ss;
    ss << line;
    while (ss >> c) {
      row.push_back(c);
    }
    grid.push_back(row);
  }
  return grid;
}

void printGrid(vector<vector<char>> grid) {
  for (int y = 0; y < grid.size(); y++) {
    for (int x = 0; x < grid[0].size(); x++) {
      cout << grid[y][x];
    }
    cout << endl;
  }
}

void plotScore(vector<vector<char>> grid, set<tuple<int,int>> &visited, int x, int y, char c, int &perimeter, int &size) {
  if (visited.count(make_tuple(x,y))) return;
  visited.insert(make_tuple(x,y));
  size++;

  // above
  if (y == 0 || grid[y - 1][x] != c) {
    perimeter++;
  } else if (!visited.count(make_tuple(x,y - 1))) {
    plotScore(grid, visited, x, y - 1, c, perimeter, size);
  }
  // below
  if (y == grid.size() - 1 || grid[y + 1][x] != c) {
    perimeter++;
  } else if (!visited.count(make_tuple(x,y + 1))) {
    plotScore(grid, visited, x, y + 1, c, perimeter, size);
  }

  // left
  if (x == 0 || grid[y][x - 1] != c) {
    perimeter++;
  } else if (!visited.count(make_tuple(x - 1,y))) {
    plotScore(grid, visited, x - 1, y, c, perimeter, size);
  }
  // right
  if (x == grid[0].size() - 1 || grid[y][x + 1] != c) {
    perimeter++;
  } else if (!visited.count(make_tuple(x + 1,y))) {
    plotScore(grid, visited, x + 1, y, c, perimeter, size);
  }
}

enum position {
  TL,
  TR,
  BL,
  BR
};

void plotScoreCheaper(vector<vector<char>> grid, set<tuple<int,int>> &visited, set<tuple<int,int,position>> &visited_corners, int x, int y, char c, int &sides, int &size) {
  if (visited.count(make_tuple(x,y))) return;
  visited.insert(make_tuple(x,y));
  size++;

  // check if grid[y][x] is a corner, since #corners == #sides
  /// top left
  if (!visited_corners.count(make_tuple(x, y, TL)) && 
    ((x == 0 || grid[y][x - 1] != c) && (y == 0 || grid[y - 1][x] != c)                            // outer corner
    || (x > 0 && y > 0 && grid[y][x - 1] == c && grid[y - 1][x] == c && grid[y - 1][x - 1] != c))) // inner corner
    {
    sides++;
    visited_corners.insert(make_tuple(x, y, TL));
  }
  /// bottom left
  if (!visited_corners.count(make_tuple(x, y, BL)) && 
    ((x == 0 || grid[y][x - 1] != c) && (y == grid.size() - 1 || grid[y + 1][x] != c))                          // outer corner
    || (x > 0 && y < grid.size() - 1 && grid[y][x - 1] == c && grid[y + 1][x] == c && grid[y + 1][x - 1] != c)) // inner corner
    {
    sides++;
    visited_corners.insert(make_tuple(x, y, BL));
  }
  /// top right
  if (!visited_corners.count(make_tuple(x, y, TR)) && 
    ((x == grid[y].size() - 1 || grid[y][x + 1] != c) && (y == 0 || grid[y - 1][x] != c))                          // outer corner
    || (x < grid[y].size() - 1 && y > 0 && grid[y][x + 1] == c && grid[y - 1][x] == c && grid[y - 1][x + 1] != c)) // inner corner
    {
    sides++;
    visited_corners.insert(make_tuple(x, y, TR));
  }
  /// bottom right
  if (!visited_corners.count(make_tuple(x, y, BR)) && 
    ((x == grid[y].size() - 1 || grid[y][x + 1] != c) && (y == grid.size() - 1 || grid[y + 1][x] != c))                          // outer corner
    || (x < grid[y].size() - 1 && y < grid.size() - 1 && grid[y][x + 1] == c && grid[y + 1][x] == c && grid[y + 1][x + 1] != c)) // inner corner
    {
    sides++;
    visited_corners.insert(make_tuple(x, y, BR));
  }

  // now recurse on all 4 sides
  if (y > 0 && !visited.count(make_tuple(x, y - 1)) && grid[y - 1][x] == c) {
    plotScoreCheaper(grid, visited, visited_corners, x, y - 1, c, sides, size);
  }
  if (y < grid.size() - 1 && !visited.count(make_tuple(x, y + 1)) && grid[y + 1][x] == c) {
    plotScoreCheaper(grid, visited, visited_corners, x, y + 1, c, sides, size);
  }
  if (x > 0 && !visited.count(make_tuple(x - 1, y)) && grid[y][x - 1] == c) {
    plotScoreCheaper(grid, visited, visited_corners, x - 1, y, c, sides, size);
  }
  if (x < grid[y].size() - 1 && !visited.count(make_tuple(x + 1, y)) && grid[y][x + 1] == c) {
    plotScoreCheaper(grid, visited, visited_corners, x + 1, y, c, sides, size);
  }
}

int part1(const char *path) {
  vector<vector<char>> grid = parseGrid(path);

  int ret = 0;

  set<tuple<int,int>> visited;
  for (int y = 0; y < grid.size(); y++) {
    for (int x = 0; x < grid[y].size(); x++) {
      int perimeter = 0;
      int size = 0;
      plotScore(grid, visited, x, y, grid[y][x], perimeter, size);
      ret += perimeter * size;
    }
  }

  return ret;
}

int part2(const char *path) {
  vector<vector<char>> grid = parseGrid(path);
  set<tuple<int,int,position>> visited_corners;

  int ret = 0;

  set<tuple<int,int>> visited;
  for (int y = 0; y < grid.size(); y++) {
    for (int x = 0; x < grid[y].size(); x++) {
      int sides = 0;
      int size = 0;
      plotScoreCheaper(grid, visited, visited_corners, x, y, grid[y][x], sides, size);
      if (sides != 0) DBG("visited " << grid[y][x] << " got sides=" << sides << " and size=" << size << " result=" << sides * size << endl);
      ret += sides * size;
    }
  }

  return ret;
}

int main(int argc, char *argv[]) {
  cout << "example1: " << part1("example") << endl;
  cout << "input1: " << part1("input") << endl;
  cout << "example2: " << part2("example") << endl;
  cout << "input2: " << part2("input") << endl;
  return 0;
}