banan-os/userspace/aoc2023/day9/main.cpp

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#include <BAN/String.h>
#include <BAN/Vector.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;
i64 parse_i64(BAN::StringView sv)
{
bool negative = (!sv.empty() && sv.front() == '-');
if (negative)
sv = sv.substring(1);
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i64 result = 0;
for (char c : sv)
{
if (!isdigit(c))
break;
result = (result * 10) + (c - '0');
}
return negative ? -result : result;
}
BAN::Vector<BAN::Vector<i64>> build_difference_tree(BAN::StringView input)
{
auto value_strs = MUST(input.split(' '));
if (value_strs.empty())
return {};
BAN::Vector<BAN::Vector<i64>> tree;
MUST(tree.emplace_back(value_strs.size(), 0));
for (size_t i = 0; i < value_strs.size(); i++)
tree.back()[i] = parse_i64(value_strs[i]);
bool all_zeroes = false;
while (!all_zeroes)
{
size_t last = tree.size();
MUST(tree.emplace_back(tree.back().size() - 1, 0));
all_zeroes = true;
for (size_t i = 0; i < tree.back().size(); i++)
{
i64 lhs = tree[last - 1][i + 0];
i64 rhs = tree[last - 1][i + 1];
tree[last][i] = rhs - lhs;
if (tree[last][i] != 0)
all_zeroes = false;
}
}
return tree;
}
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i64 puzzle1(FILE* fp)
{
i64 result = 0;
char buffer[128];
while (fgets(buffer, sizeof(buffer), fp))
{
auto tree = build_difference_tree(buffer);
if (tree.empty())
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continue;
i64 current = 0;
for (size_t i = tree.size(); i > 0; i--)
current = tree[i - 1].back() + current;
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result += current;
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}
return result;
}
i64 puzzle2(FILE* fp)
{
i64 result = 0;
char buffer[128];
while (fgets(buffer, sizeof(buffer), fp))
{
auto tree = build_difference_tree(buffer);
if (tree.empty())
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continue;
i64 current = 0;
for (size_t i = tree.size(); i > 0; i--)
current = tree[i - 1].front() - current;
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result += current;
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}
return result;
}
int main(int argc, char** argv)
{
const char* file_path = "/usr/share/aoc2023/day9_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);
}