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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>
T
solve_rec(const vector<T>& values)
{
vector<T> differences;
for ( size_t idx = 1; idx < values.size(); ++idx ) {
differences.emplace_back(values[idx] - values[idx - 1]);
}
auto all_zeros = all_of(differences.begin(), differences.end(), [](T diff) { return diff == 0; });
if ( !all_zeros ) {
return solve_rec(differences) + values.back();
}
else {
return values.back();
}
}
void
part1(const vector<string>& lines)
{
long sum = 0;
for ( const auto& line: lines ) {
sum += solve_rec(read_ints(line));
}
cout << sum << endl;
}
void
part2(const vector<string>& lines)
{
long sum = 0;
for ( const auto& line: lines ) {
auto values = read_ints(line);
reverse(values.begin(), values.end());
sum += solve_rec(values);
}
cout << sum << endl;
}
int
main()
{
auto lines = read_file("data/day09.txt");
part1(lines);
part2(lines);
}
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