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#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
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;
}
template<typename T = long>
vector<T>
read_ints(const string& line)
{
stringstream iss{ line };
return vector<T>{ istream_iterator<T>{ iss }, istream_iterator<T>{} };
}
template<typename T>
void
solve_rec_part1(vector<T>& values)
{
vector<T> differences;
for ( size_t idx = 1; idx < values.size(); ++idx ) {
auto difference = values[idx] - values[idx - 1];
differences.emplace_back(difference);
}
auto all_zeros = all_of(differences.begin(), differences.end(), [](long diff) { return diff == 0; });
if ( !all_zeros) {
solve_rec_part1(differences);
}
else {
differences.emplace_back(0);
}
auto last_value = values.back();
auto last_difference = differences.back();
values.emplace_back(last_value + last_difference);
}
void
part1()
{
auto lines = read_file("data/day09.txt");
long sum = 0;
for ( const auto& line: lines ) {
auto values = read_ints(line);
solve_rec_part1(values);
sum += values.back();
}
cout << sum << endl;
}
template<typename T>
void
solve_rec_part2(vector<T>& values)
{
vector<T> differences;
for ( size_t idx = 1; idx < values.size(); ++idx ) {
auto difference = values[idx] - values[idx - 1];
differences.emplace_back(difference);
}
auto all_zeros = all_of(differences.begin(), differences.end(), [](long diff) { return diff == 0; });
if ( !all_zeros) {
solve_rec_part2(differences);
}
else {
differences.insert(differences.begin(), 0);
}
auto first_value = values.front();
auto first_difference = differences.front();
values.insert(values.begin(), first_value - first_difference);
}
void
part2()
{
auto lines = read_file("data/day09.txt");
long sum = 0;
for ( const auto& line: lines ) {
auto values = read_ints(line);
solve_rec_part2(values);
sum += values.front();
}
cout << sum << endl;
}
int
main()
{
part1();
part2();
}
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