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#include <cstdlib>
#include <fstream>
#include <iostream>
#include <map>
#include <set>
#include <vector>
using namespace std;
vector<unsigned long>
read_file(string_view filename)
{
fstream input{ filename };
vector<unsigned long> lines;
for ( unsigned long value{}; input >> value; ) {
lines.emplace_back(value);
}
return lines;
}
unsigned long
step(unsigned long value)
{
// compiler will optimize these calculations
value = (value ^ (value * 64)) % 16777216;
value = (value ^ (value / 32)) % 16777216;
value = (value ^ (value * 2048)) % 16777216;
return value;
}
void
part1(const vector<unsigned long>& values)
{
unsigned long sum = 0;
for ( auto value: values ) {
for ( int i = 0; i != 2000; ++i ) {
value = step(value);
}
sum += value;
}
cout << sum << endl;
}
void
part2(const vector<unsigned long>& values)
{
using seq_type = tuple<unsigned long, unsigned long, unsigned long, unsigned long>;
map<seq_type, unsigned long> total;
for ( auto value: values ) {
vector<unsigned long> list{ value % 10 };
for ( int i = 0; i != 2000; ++i ) {
value = step(value);
list.emplace_back(value % 10);
}
set<seq_type> seen;
for ( size_t idx = 4; idx < list.size(); ++idx ) {
const auto a = list[idx - 4];
const auto b = list[idx - 3];
const auto c = list[idx - 2];
const auto d = list[idx - 1];
const auto e = list[idx];
seq_type seq{ b - a, c - b, d - c, e - d };
if ( seen.contains(seq) ) {
continue;
}
seen.insert(seq);
total[seq] += e;
}
}
cout << ranges::max_element(total, [](const auto& lhs, const auto& rhs) { return lhs.second < rhs.second; })->second << endl;
}
int
main()
{
auto data = read_file("data/day22.txt");
part1(data);
part2(data);
}
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