Advent of Code 2025, done in C++
bpavuk.neocities.org
1#include "common/getinputpath.h"
2#include <algorithm>
3#include <fstream>
4#include <print>
5#include <string>
6#include <vector>
7
8#ifndef DATA_FOLDER
9#error "DATA_FOLDER is not defined. Check Meson configuration."
10#endif // !DATA_FOLDER
11
12char biggest_char_available(std::string input, int reserved_begin,
13 int reserved_end) {
14 std::string substring = input.substr(
15 reserved_begin, input.length() - reserved_end - reserved_begin);
16 std::vector<char> chars(substring.begin(), substring.end());
17 std::vector<char> chars_sorted(chars);
18 std::sort(chars_sorted.begin(), chars_sorted.end());
19 std::reverse(chars_sorted.begin(), chars_sorted.end());
20
21 auto idx_of_biggest = substring.find_first_of(chars_sorted[0]);
22 return chars[idx_of_biggest];
23}
24
25// runtime on Ryzen 5 5600G: 0.005s
26int main() {
27 std::ifstream file(get_input_path(DATA_FOLDER));
28 if (!file.is_open()) {
29 std::println("Could not open the file!");
30 return 1;
31 }
32
33 long long password_part_1 = 0;
34 long long password_part_2 = 0;
35
36 for (std::string t; std::getline(file, t);) {
37 // part 1
38 {
39 auto tens = biggest_char_available(t, 0, 1);
40 auto tens_idx = t.find_first_of(tens);
41
42 auto ones = biggest_char_available(t, tens_idx + 1, 0);
43
44 std::string result_str = std::string() + tens + ones;
45 long long result = std::stoll(result_str);
46 std::println("{}", result_str);
47
48 password_part_1 += result;
49 }
50
51 // part 2
52 {
53 int reserved_begin = 0;
54 std::string result{};
55 for (int reserved_end = 11; reserved_end >= 0; --reserved_end) {
56 auto ch = biggest_char_available(t, reserved_begin, reserved_end);
57 reserved_begin += t.substr(reserved_begin).find_first_of(ch) + 1;
58 result += ch;
59 }
60 std::println("p2: {}", result);
61 password_part_2 += std::stoll(result);
62 }
63 }
64 std::println("Eureka! {} / {}", password_part_1, password_part_2);
65 return 0;
66}