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#include <algorithm>
#include <array>
#include <fstream>
#include <functional>
#include <iostream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
using position_t = tuple<size_t, size_t>;
vector<string>
read_file(string_view filename)
{
fstream input{ filename };
vector<string> data;
for ( string line; getline(input, line); ) {
data.emplace_back(line);
}
return data;
}
set<position_t>
get_neighbours(const vector<string>& maze, position_t possition)
{
static const position_t deltas[] = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } }; // NOLINT
static const auto SYM_UP = '^';
static const auto SYM_RIGHT = '>';
static const auto SYM_DOWN = 'v';
static const auto SYM_LEFT = '<';
const auto [row, col] = possition;
switch ( maze[row][col] ) {
case SYM_UP:
return { make_tuple(row - 1, col) };
case SYM_RIGHT:
return { make_tuple(row, col + 1) };
case SYM_DOWN:
return { make_tuple(row + 1, col) };
case SYM_LEFT:
return { make_tuple(row, col - 1) };
}
set<position_t> positions;
for ( const auto& delta: deltas ) {
const auto new_row = row + get<0>(delta);
const auto new_col = col + get<1>(delta);
if ( new_row >= maze.size() || new_col >= maze[0].size() ) {
continue;
}
if ( maze[new_row][new_col] == '#' ) {
continue;
}
if ( new_row < row && maze[new_row][new_col] == SYM_DOWN ) {
continue;
}
if ( new_row > row && maze[new_row][new_col] == SYM_UP ) {
continue;
}
if ( new_col < col && maze[new_row][new_col] == SYM_RIGHT ) {
continue;
}
if ( new_col > col && maze[new_row][new_col] == SYM_LEFT ) {
continue;
}
positions.emplace(new_row, new_col);
}
return positions;
}
set<position_t>
get_neighbours2(const vector<string>& maze, position_t possition)
{
static const position_t deltas[] = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } }; // NOLINT
const auto [row, col] = possition;
set<position_t> positions;
for ( const auto& delta: deltas ) {
const auto new_row = row + get<0>(delta);
const auto new_col = col + get<1>(delta);
if ( new_row >= maze.size() || new_col >= maze[0].size() ) {
continue;
}
if ( maze[new_row][new_col] == '#' ) {
continue;
}
positions.emplace(new_row, new_col);
}
return positions;
}
void
solve(const vector<string>& maze, function<set<position_t>(const vector<string>&, position_t)> neighbours)
{
const position_t start = { 0, maze[0].find('.') };
const position_t end = { maze.size() - 1, maze[maze.size() - 1].find('.') };
vector<vector<bool>> visited(maze.size(), vector<bool>(maze[0].size()));
function<long(position_t, long)> find_longest_path = [&](position_t position, long current) -> long {
const auto [row, col] = position;
if ( visited[row][col] ) {
return 0;
}
if ( position == end ) {
return current;
}
long value = 0;
visited[row][col] = true;
for ( const auto& neighbour: neighbours(maze, position) ) {
value = max(value, find_longest_path(neighbour, current + 1));
}
visited[row][col] = false;
return value;
};
auto value = find_longest_path(start, 0);
cout << value << endl;
}
int
main()
{
const auto maze = read_file("data/day23.txt");
solve(maze, get_neighbours);
solve(maze, get_neighbours2);
}
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