banan-os/userspace/aoc2023/day8/main.cpp

132 lines
2.6 KiB
C++

#include <BAN/HashMap.h>
#include <BAN/String.h>
#include <ctype.h>
#include <stdio.h>
#include <stdint.h>
using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
static u32 coord_to_u32(BAN::StringView coord)
{
ASSERT(coord.size() == 3);
return ((u32)coord[2] << 16) | ((u32)coord[1] << 8) | (u32)coord[0];
}
i64 puzzle1(FILE* fp)
{
BAN::HashMap<u32, u32[2]> targets;
BAN::String left_right_path;
{
char buffer[512];
if (!fgets(buffer, sizeof(buffer), fp))
return -1;
MUST(left_right_path.append(buffer));
left_right_path.pop_back();
if (!fgets(buffer, sizeof(buffer), fp))
return -1;
while (fgets(buffer, sizeof(buffer), fp))
{
BAN::StringView line(buffer);
if (line.size() < 15)
continue;
MUST(targets.emplace(
coord_to_u32(line.substring(0, 3)),
coord_to_u32(line.substring(7, 3)),
coord_to_u32(line.substring(12, 3))
));
}
}
u32 current = coord_to_u32("AAA"sv);
u32 target = coord_to_u32("ZZZ"sv);
i64 steps = 0;
for (; current != target; steps++)
{
char direction = left_right_path[steps % left_right_path.size()];
current = targets[current][direction == 'R'];
}
return steps;
}
i64 puzzle2(FILE* fp)
{
BAN::HashMap<u32, u32[2]> targets;
BAN::String left_right_path;
{
char buffer[512];
if (!fgets(buffer, sizeof(buffer), fp))
return -1;
MUST(left_right_path.append(buffer));
left_right_path.pop_back();
if (!fgets(buffer, sizeof(buffer), fp))
return -1;
while (fgets(buffer, sizeof(buffer), fp))
{
BAN::StringView line(buffer);
if (line.size() < 15)
continue;
MUST(targets.emplace(
coord_to_u32(line.substring(0, 3)),
coord_to_u32(line.substring(7, 3)),
coord_to_u32(line.substring(12, 3))
));
}
}
i64 result = 1;
for (auto [key, _] : targets)
{
if ((key >> 16) != 'A')
continue;
i64 steps = 0;
for (u32 pos = key; (pos >> 16) != 'Z'; steps++)
{
char direction = left_right_path[steps % left_right_path.size()];
pos = targets[pos][direction == 'R'];
}
// Calculating LCM of all steps only works if steps is a multiple of full path size.
// This seems to be the case with my input, but it's good to verify...
ASSERT(steps % left_right_path.size() == 0);
result = BAN::Math::lcm(result, steps);
}
return result;
}
int main(int argc, char** argv)
{
const char* file_path = "/usr/share/aoc2023/day8_input.txt";
if (argc >= 2)
file_path = argv[1];
FILE* fp = fopen(file_path, "r");
if (fp == nullptr)
{
perror("fopen");
return 1;
}
printf("puzzle1: %lld\n", puzzle1(fp));
fseek(fp, 0, SEEK_SET);
printf("puzzle2: %lld\n", puzzle2(fp));
fclose(fp);
}