banan-os/userspace/aoc2023/day17/main.cpp

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2023-12-23 18:46:43 +02:00
#include <BAN/HashSet.h>
#include <BAN/Vector.h>
#include <BAN/Hash.h>
#include <ctype.h>
#include <inttypes.h>
#include <stdio.h>
using i8 = int8_t;
using i16 = int16_t;
using i32 = int32_t;
using i64 = int64_t;
using u8 = uint8_t;
using u16 = uint16_t;
using u32 = uint32_t;
using u64 = uint64_t;
struct Position
{
i64 x;
i64 y;
bool operator==(const Position& other) const
{
return x == other.x && y == other.y;
}
};
namespace BAN
{
template<>
struct hash<Position>
{
hash_t operator()(const Position& position) const
{
return hash<u64>()(((u64)position.x << 32) | (u64)position.y);
}
};
}
BAN::Vector<BAN::Vector<i64>> parse_grid(FILE* fp)
{
BAN::Vector<BAN::Vector<i64>> grid;
char buffer[256];
while (fgets(buffer, sizeof(buffer), fp))
{
BAN::StringView line(buffer);
ASSERT(line.back() == '\n');
line = line.substring(0, line.size() - 1);
if (line.empty())
break;
MUST(grid.emplace_back(line.size()));
for (size_t i = 0; i < line.size(); i++)
grid.back()[i] = line[i] - '0';
}
return grid;
}
//static constexpr i64 MIN_STEPS = 4;
//static constexpr i64 MAX_STEPS = 10;
template<i64 MIN_STEPS, i64 MAX_STEPS>
i64 solve_general(FILE* fp)
{
struct Block
{
// heatloss[x][y]:
// x: direction
// y: steps left in that direction
i64 heatloss[4][MAX_STEPS + 1];
i8 entered_from = -1;
};
const auto grid = parse_grid(fp);
// initially mark everything very large, except (0, 0)
BAN::Vector<BAN::Vector<Block>> heatloss_map;
MUST(heatloss_map.resize(grid.size()));
for (size_t y = 0; y < grid.size(); y++)
{
MUST(heatloss_map[y].resize(grid[y].size()));
for (size_t x = 0; x < grid[y].size(); x++)
for (size_t dir = 0; dir < 4; dir++)
for (size_t step = 0; step <= MAX_STEPS; step++)
heatloss_map[y][x].heatloss[dir][step] = 1'000'000'000;
}
for (size_t dir = 0; dir < 4; dir++)
for (size_t step = 0; step <= MAX_STEPS; step++)
heatloss_map[0][0].heatloss[dir][step] = 0;
BAN::HashSet<Position> visited;
BAN::HashSet<Position> pending;
MUST(pending.insert({ 0, 0 }));
while (!pending.empty())
{
auto position = *pending.begin();
pending.remove(position);
Position offsets[4] = { { -1, 0 }, { 0, -1 }, { 1, 0 }, { 0, 1 } };
for (i8 dir = 0; dir < 4; dir++)
{
auto target = position;
i64 path_heatloss = 0;
auto is_target_in_bounds =
[&](const Position& target)
{
if (target.y < 0 || target.y >= (i64)grid.size())
return false;
if (target.x < 0 || target.x >= (i64)grid.front().size())
return false;
return true;
};
i64 target_distance = (heatloss_map[position.y][position.x].entered_from == dir) ? 1 : MIN_STEPS;
for (i64 i = 0; i < target_distance; i++)
{
target.x += offsets[dir].x;
target.y += offsets[dir].y;
if (!is_target_in_bounds(target))
break;
path_heatloss += grid[target.y][target.x];
}
if (!is_target_in_bounds(target))
continue;
auto& target_heatloss = heatloss_map[target.y][target.x];
bool target_updated = false;
for (i8 new_dir = 0; new_dir < 4; new_dir++)
{
// Don't allow going backwards
if (new_dir == dir + 2 || dir == new_dir + 2)
continue;
for (i64 step = target_distance; step <= MAX_STEPS; step++)
{
i64 possible_heatloss = heatloss_map[position.y][position.x].heatloss[dir][step] + path_heatloss;
i64 new_dir_max_step = (new_dir == dir) ? step - target_distance : MAX_STEPS;
for (i64 i = 0; i <= new_dir_max_step; i++)
{
if (possible_heatloss >= target_heatloss.heatloss[new_dir][i])
continue;
target_heatloss.heatloss[new_dir][i] = possible_heatloss;
target_heatloss.entered_from = dir;
target_updated = true;
}
}
}
if (target_updated || !visited.contains(target))
MUST(pending.insert(target));
}
MUST(visited.insert(position));
}
i64 result = INT64_MAX;
for (size_t dir = 0; dir < 4; dir++)
for (size_t step = 0; step <= MAX_STEPS; step++)
result = BAN::Math::min(result, heatloss_map.back().back().heatloss[dir][step]);
return result;
}
i64 puzzle1(FILE* fp)
{
return solve_general<1, 3>(fp);
}
i64 puzzle2(FILE* fp)
{
return solve_general<4, 10>(fp);
}
int main(int argc, char** argv)
{
const char* file_path = "/usr/share/aoc2023/day17_input.txt";
if (argc >= 2)
file_path = argv[1];
FILE* fp = fopen(file_path, "r");
if (fp == nullptr)
{
perror("fopen");
return 1;
}
printf("puzzle1: %" PRId64 "\n", puzzle1(fp));
fseek(fp, 0, SEEK_SET);
printf("puzzle2: %" PRId64 "\n", puzzle2(fp));
fclose(fp);
}