aoc24/10/main.cc

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

using namespace std;

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

  ifstream input(path);
  string line;
  while (getline(input, line)) {
    char c;
    vector<int> row;
    stringstream ss;
    ss << line;
    while (ss >> c) {
      int num = c - '0';
      row.push_back(num);
    }
    grid.push_back(row);
  }
  return grid;
}

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

int trailheadHelper(vector<vector<int>> grid, int y, int x, set<tuple<int,int>, greater<tuple<int,int>>> &visited) {
  int curr = grid[y][x];

  // base case
  if (curr == 9) {
    if (visited.count(make_tuple(y,x))) {
      return 0;
    } else {
      visited.insert(make_tuple(y,x));
      return 1;
    }
  }

  int sum = 0;

  // try each direction
  if (x > 0 && grid[y][x - 1] == grid[y][x] + 1) {
    sum += trailheadHelper(grid, y, x - 1, visited);
  }
  if (x < grid[y].size() - 1 && grid[y][x + 1] == grid[y][x] + 1) {
    sum += trailheadHelper(grid, y, x + 1, visited);
  }
  if (y > 0 && grid[y - 1][x] == grid[y][x] + 1) {
    sum += trailheadHelper(grid, y - 1, x, visited);
  }
  if (y < grid.size() - 1 && grid[y + 1][x] == grid[y][x] + 1) {
    sum += trailheadHelper(grid, y + 1, x, visited);
  }

  return sum;
}

int trailheadCount(vector<vector<int>> grid, int y, int x) {
  set<tuple<int,int>, greater<tuple<int,int>>> visited;

  return trailheadHelper(grid, y, x, visited);
}

int trailheadCount2(vector<vector<int>> grid, int y, int x) {
  int curr = grid[y][x];

  // base case
  if (curr == 9) {
    return 1;
  }

  int sum = 0;

  // try each direction
  if (x > 0 && grid[y][x - 1] == grid[y][x] + 1) {
    sum += trailheadCount2(grid, y, x - 1);
  }
  if (x < grid[y].size() - 1 && grid[y][x + 1] == grid[y][x] + 1) {
    sum += trailheadCount2(grid, y, x + 1);
  }
  if (y > 0 && grid[y - 1][x] == grid[y][x] + 1) {
    sum += trailheadCount2(grid, y - 1, x);
  }
  if (y < grid.size() - 1 && grid[y + 1][x] == grid[y][x] + 1) {
    sum += trailheadCount2(grid, y + 1, x);
  }

  return sum;
}


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

  int sum = 0;
  for (int y = 0; y < grid.size(); y++) {
    for (int x = 0; x < grid[0].size(); x++) {
      if (grid[y][x] == 0) {
        sum += trailheadCount(grid, y, x);
      }
    }
  }
  return sum;
}

int part2(const char *path) {
  vector<vector<int>> grid = parseGrid(path);

  int sum = 0;
  for (int y = 0; y < grid.size(); y++) {
    for (int x = 0; x < grid[0].size(); x++) {
      if (grid[y][x] == 0) {
        sum += trailheadCount2(grid, y, x);
      }
    }
  }
  return sum;
}

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;
}