do day 2

build

@@ -0,0 +1,4 @@
+#!/bin/bash
+
+set -e
+g++ src/day$1.cpp -std=c++23 -g3

dbg

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+set -e
+./build $1
+gdb a.out

run

@@ -2,5 +2,5 @@
 
 set -e
 
-g++ src/day$1.cpp -std=c++23
+./build $1
 ./a.out

src/day2.cpp

@@ -0,0 +1,85 @@
+// :autocmd BufWritePost *.cpp :silent exec "!./build 2"
+#include <fstream>
+#include <iostream>
+#include <numeric>
+#include <string>
+#include <vector>
+
+struct Data {
+  int64_t min;
+  int64_t max;
+};
+
+using std::cout, std::endl, std::vector, std::ifstream;
+
+int64_t part_1(const vector<Data> &);
+unsigned long long part_2(const vector<Data> &);
+
+int main() {
+  ifstream file{"input/2025-2.txt"};
+  Data line;
+  char throwaway;
+  vector<Data> v;
+  while (file >> line.min >> throwaway >> line.max) {
+    v.push_back(line);
+    file >> throwaway;
+  }
+  cout << "Part 1: " << part_1(v) << endl;
+  cout << "Part 2: " << part_2(v) << endl;
+}
+
+int64_t part_1(const vector<Data> &v) {
+  int64_t answer{0};
+  for (auto d : v) {
+    for (auto n{d.min}; n <= d.max; ++n) {
+      auto temp{std::to_string(n)};
+      auto lhs{temp.substr(0, (temp.size() / 2))};
+      auto rhs{temp.substr(lhs.size())};
+      if (lhs == rhs) {
+        answer += std::stoll(lhs + rhs);
+      }
+    }
+  }
+  return answer;
+}
+
+int64_t solve_n(int64_t n) {
+  auto n_str{std::to_string(n)};
+  for (size_t i{1}; i <= n_str.size() / 2; ++i) {
+    auto lhs{n_str.substr(0, i)};
+    if (n_str.size() % lhs.size() == 0) {
+      int64_t repeat_cnt = n_str.size() / lhs.size();
+      std::string comparator{""};
+      for (auto i{0}; i < repeat_cnt; ++i) {
+        comparator += lhs;
+      }
+      if (comparator == n_str) {
+        return n;
+      }
+    }
+  }
+  return 0;
+}
+
+unsigned long long part_2(const vector<Data> &v) {
+  unsigned long long ans{0};
+  for (auto d : v) {
+    for (auto n{d.min}; n <= d.max; ++n) {
+      ans += solve_n(n);
+    }
+  }
+
+  // todo: dead code, delete me
+  unsigned long long foobar = std::accumulate(v.begin(), v.end(), 0, [&ans](unsigned long long acc, Data d) {
+    for (auto n{d.min}; n <= d.max; ++n) {
+          acc += solve_n(n);
+    }
+    return acc;
+  });
+
+  // help please :)
+  // why ans != foobar? looks like same but not same
+  // stepping through with debugger, it even seems the same on last iteration of accumulate
+
+  return ans;
+}