aoc24: day02b complete

sol/24/day01.cpp

@@ -0,0 +1,68 @@
+#include <numeric>
+#include <algorithm>
+
+#include "aoc.hpp"
+#include "aoc/utils.hpp"
+#include "fmt/format.h"
+
+auto aoc24::day01([[maybe_unused]]std::span<char const*> const& args) -> std::expected<void, aoc::error> {
+    constexpr auto filename = "./dat/24/re/01.txt";
+    std::ifstream strm{filename, std::ios::in};
+    if (!strm.is_open()) {
+        return aoc::make_error(
+                fmt::format("Error opening file: {}\n", filename),
+                std::errc::file_exists
+            );
+    }
+
+    std::vector<std::uint32_t> a{};
+    std::vector<std::uint32_t> b{};
+
+    std::string str{};
+    while (strm) {
+        auto const c = char(strm.peek());
+        if (std::isdigit(c)) {
+            str += char(strm.get());
+            continue;
+        }
+        if (c == ' ') {
+            if (!str.empty()) {
+                a.emplace_back(std::stoi(str));
+                str.clear();
+            }
+        }
+        if (c == '\n') {
+            if (!str.empty()) {
+                b.emplace_back(std::stoi(str));
+                str.clear();
+            }
+        }
+        [[discard]]strm.get();
+    }
+
+    fmt::print("a: {}, b: {}\n", a.size(), b.size());
+
+    std::sort(std::begin(a), std::end(a));
+    std::sort(std::begin(b), std::end(b));
+
+    auto diff_view = std::views::zip(a, b) | std::views::transform([](auto const& p) {
+        auto const [x, y] = p;
+        return x > y ? x - y : y - x;
+    });
+    auto const sum = std::accumulate(std::begin(diff_view), std::end(diff_view), 0);
+
+    fmt::print("Part A: {}\n", std::abs(sum));
+
+    auto values = a | std::views::transform([&b](auto v) {
+        return std::pair{v, b | std::views::filter([v](auto c) {
+            return v == c; // Filter elements in `b` equal to `v`
+        }) | std::ranges::to<std::vector>()};
+    }) | std::ranges::to<std::vector>();
+
+    auto const meow = std::accumulate(std::begin(values), std::end(values), 0, [](auto const acc, auto const& pair) {
+        return acc + std::int32_t(pair.first * pair.second.size());
+    });
+
+    fmt::print("Part B: {}\n", meow);
+    return {};
+}