finish day 3

day3.cpp

@@ -0,0 +1,79 @@
+//
+// Created by Grant Horner on 12/3/25.
+//
+
+#include <ranges>
+#include <string>
+#include <fstream>
+#include <sstream>
+#include "doctest.h"
+
+namespace day3 {
+const std::string sample = "987654321111111\n"
+        "811111111111119\n"
+        "234234234234278\n"
+        "818181911112111\n";
+
+auto split_into_banks(const std::string_view input) {
+    return std::views::split(input, '\n')
+           | std::views::filter([](const auto &s) {
+               return !s.empty();
+           })
+           | std::views::transform([](const auto &x) {
+               return std::string_view(x);
+           });
+}
+
+uint64_t solve(const std::string_view input, uint8_t num_batteries) {
+    uint64_t sum = 0;
+    for (auto split: split_into_banks(input)) {
+        uint64_t bank = 0;
+        size_t largest_index = 0;
+        for (size_t i = num_batteries; i > 0; i--) {
+            const auto num_reserved = i - 1;
+            const auto substr_len = split.size() - largest_index - num_reserved;
+            const auto not_last = split.substr(largest_index, substr_len);
+
+            size_t temp_largest_index = 0;
+            uint8_t largest = 0;
+            for (size_t j = 0; j < not_last.size(); j++) {
+                if (const char c = not_last[j]; c > largest) {
+                    largest = c;
+                    temp_largest_index = 1 + j;
+                }
+            }
+            largest_index += temp_largest_index;
+            bank += (largest - '0') * std::pow(10, i - 1);
+        }
+        sum += bank;
+    }
+
+    return sum;
+}
+
+TEST_SUITE_BEGIN("Day 3");
+
+TEST_CASE("solve first sample") {
+    CHECK(solve(sample, 2) == 357);
+}
+
+TEST_CASE("solve first puzzle") {
+    std::ifstream input("day3input.txt");
+    std::stringstream buf;
+    buf << input.rdbuf();
+    CHECK(solve(buf.view(),2) == 17095);
+}
+
+TEST_CASE("solve second sample") {
+    CHECK(solve(sample, 12) == 3121910778619);
+}
+
+TEST_CASE("solve second input") {
+    std::ifstream input("day3input.txt");
+    std::stringstream buf;
+    buf << input.rdbuf();
+    CHECK(solve(buf.view(), 12) == 168794698570517);
+}
+
+TEST_SUITE_END();
+}