2025 day 1: solve part 1

Author: yut23

2025/answer_tests/day01/example1.txt

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+Day 1:
+3

2025/input/day01/example1.txt

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+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82

2025/src/day01.cpp

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+/******************************************************************************
+ * File:        day01.cpp
+ *
+ * Author:      Eric T. Johnson (yut23)
+ * Created:     2025-12-01
+ *****************************************************************************/
+
+#include "day01.hpp"
+#include "lib.hpp"
+#include <fstream>  // for ifstream
+#include <iostream> // for cout
+
+int main(int argc, char **argv) {
+    std::ifstream infile = aoc::parse_args(argc, argv).infile;
+
+    auto rotations = aoc::day01::read_input(infile);
+
+    int dial = 50;
+    int part1 = 0;
+    for (const auto rot : rotations) {
+        dial += rot;
+        dial %= 100;
+        if (dial == 0) {
+            ++part1;
+        }
+    }
+
+    std::cout << part1 << "\n";
+
+    return 0;
+}

2025/src/day01.hpp

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+/******************************************************************************
+ * File:        day01.hpp
+ *
+ * Author:      Eric T. Johnson (yut23)
+ * Created:     2025-12-01
+ *****************************************************************************/
+
+#ifndef DAY01_HPP_XFIW6CVE
+#define DAY01_HPP_XFIW6CVE
+
+#include <iostream> // for istream
+#include <string>   // for string, getline
+#include <vector>   // for vector
+
+namespace aoc::day01 {
+
+auto read_input(std::istream &is) {
+    // read file line-by-line
+    std::string line;
+    std::vector<int> rotations;
+    while (std::getline(is, line)) {
+        int rotation = std::atoi(line.c_str() + 1);
+        if (line[0] == 'L') {
+            rotation *= -1;
+        }
+        rotations.push_back(rotation);
+    }
+    return rotations;
+}
+
+} // namespace aoc::day01
+
+#endif /* end of include guard: DAY01_HPP_XFIW6CVE */