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#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
string
read_file(string_view filename)
{
fstream input{ filename };
return { istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} };
}
vector<string>
split(string_view line, string_view delimiter)
{
size_t pos_start = 0;
size_t pos_end = 0;
vector<string> res;
while ( (pos_end = line.find(delimiter, pos_start)) != std::string::npos ) {
auto token = line.substr(pos_start, pos_end - pos_start);
pos_start = pos_end + delimiter.length();
res.emplace_back(token);
}
res.emplace_back(line.substr(pos_start));
return res;
}
vector<string>
transpose(const vector<string>& lines)
{
vector<string> result(lines[0].size());
for ( const auto& line: lines ) {
for ( size_t i = 0; i < line.size(); ++i ) {
result[i] += line[i];
}
}
return result;
}
long
find_mirror(const vector<string>& input)
{
for ( size_t idx = 1; idx < input.size(); ++idx ) {
bool equal = true;
for ( size_t cnt = 0; cnt != min(idx, input.size() - idx); ++cnt ) {
if ( !(input[idx + cnt] == input[idx - 1 - cnt]) ) {
equal = false;
break;
}
}
if ( equal ) {
return long(idx);
}
}
return 0;
}
long
count_differences(string_view str1, string_view str2)
{
long diffs = 0;
for ( size_t idx = 0; idx != str1.size(); ++idx ) {
diffs += long(str1[idx] != str2[idx]);
}
return diffs;
}
long
find_mirror_part2(const vector<string>& input)
{
for ( size_t idx = 1; idx < input.size(); ++idx ) {
long errs = 0;
for ( size_t i = 0; i != min(idx, input.size() - idx); ++i ) {
errs += count_differences(input[idx + i], input[idx - 1 - i]);
}
if ( errs == 1 ) {
return long(idx);
}
}
return 0;
}
void
solve(const function<long(const vector<string>&)>& find_mirror)
{
static const long multiplier = 100;
auto contents = read_file("data/day13.txt");
auto parts = split(contents, "\n\n");
long sum = 0;
for ( const auto& part: parts ) {
auto lines = split(part, "\n");
sum += find_mirror(transpose(lines));
sum += find_mirror(lines) * multiplier;
}
cout << sum << endl;
}
int
main()
{
solve(find_mirror);
solve(find_mirror_part2);
}
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