[Hacker Rank] Warmup: Time Conversion solved ✅

docs/hackerrank/warmup/time_conversion.md

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+# [Time Conversion](https://www.hackerrank.com/challenges/time-conversion)
+
+Difficulty: #easy
+Category: #warmup
+
+Given a time in
+12-[hour AM/PM format](https://en.wikipedia.org/wiki/12-hour_clock),
+convert it to military (24-hour) time.
+
+Note:
+
+- 12:00:00AM on a 12-hour clock is 00:00:00 on a 24-hour clock.
+- 12:00:00PM on a 12-hour clock is 12:00:00 on a 24-hour clock.
+
+## Example
+
+- s = '12:01:00PM' \
+  Return '12:01:00'
+- s = '12:01:00AM' \
+  Return '00:01:00'
+
+## Function Description
+
+Complete the timeConversion function in the editor below.
+It should return a new string representing the input time in 24 hour format
+timeConversion has the following parameter(s):
+
+- string s: a time in 12 hour format
+
+## Returns
+
+- string: the time in 24 hour format
+
+## Input Format
+
+A single string s that represents a time in 12-hour clock format
+(i.e.: hh_mm_ssAM or hh:mm:ssPM).
+
+## Constraints
+
+- All input times are valid
+
+## Sample Input 0
+
+```text
+07:05:45PM
+```
+
+## Sample Output 0
+
+```text
+19:05:45
+```

src/lib/exercises/include/exercises/hackerrank/warmup/time_conversion.hpp

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+#pragma once
+
+#include <string>
+
+namespace hackerrank::warmup {
+
+std::string firstN(const std::string_view &input, unsigned long n);
+std::string lastN(const std::string_view &input, unsigned long n);
+
+std::string timeConversion(const std::string &s);
+
+} // namespace hackerrank::warmup

src/lib/exercises/src/hackerrank/warmup/time_conversion.cpp

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+#include <exercises/hackerrank/warmup/time_conversion.hpp>
+
+/**
+ * @link Problem definition [[docs/hackerrank/warmup/time_conversion.md]]
+ */
+
+#include <iomanip>
+#include <sstream>
+#include <string>
+#include <vector>
+
+namespace hackerrank::warmup {
+
+std::string firstN(const std::string_view &input, unsigned long n) {
+  unsigned long inputSize = input.size();
+  return static_cast<std::string>((n > 0 && inputSize > n) ? input.substr(0, n)
+                                                           : "");
+}
+
+std::string lastN(const std::string_view &input, unsigned long n) {
+  unsigned long inputSize = input.size();
+  return static_cast<std::string>(
+      (n > 0 && inputSize > n) ? input.substr(inputSize - n) : "");
+}
+
+std::string timeConversion(const std::string &s) {
+  char TIME_SEPARATOR = ':';
+  std::string meridian = lastN(s, 2);
+
+  auto time_str = std::stringstream(firstN(s, s.size() - 2));
+  std::string segment;
+  std::vector<std::string> time;
+
+  while (std::getline(time_str, segment, TIME_SEPARATOR)) {
+    time.push_back(segment);
+  }
+
+  std::stringstream hour_str;
+  hour_str << time[0];
+
+  int hour;
+  hour_str >> hour;
+
+  if (hour >= 12) {
+    hour = 0;
+  }
+
+  if (meridian.compare("PM") == 0) {
+    hour += 12;
+  }
+
+  hour_str.str("");
+  hour_str.clear();
+  hour_str << std::setfill('0') << std::setw(2) << hour;
+  time[0] = hour_str.str();
+
+  std::string conversion;
+  unsigned long tsize = time.size();
+  for (int i = 0; i < tsize; i++) {
+    conversion += time[i];
+    if (i < tsize - 1) {
+      conversion += ":";
+    }
+  }
+
+  return conversion;
+}
+
+} // namespace hackerrank::warmup

src/tests/unit/lib/hackerrank/warmup/test_conversion.test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include <exercises/hackerrank/warmup/time_conversion.hpp>
+#include <filesystem>
+#include <fstream>
+#include <nlohmann/json.hpp>
+#include <vector>
+
+using json = nlohmann::json;
+
+TEST_CASE("time_conversion JSON Test Cases",
+          "[hackerrank] [jsontestcase] [warmup]") {
+  std::filesystem::path cwd = std::filesystem::current_path();
+  std::string path =
+      cwd.string() +
+      "/unit/lib/hackerrank/warmup/time_conversion.testcases.json";
+
+  INFO("time_conversion JSON test cases FILE: " << path);
+
+  std::ifstream f(path);
+  json data = json::parse(f);
+
+  for (auto testcase : data) {
+    std::string result = hackerrank::warmup::timeConversion(testcase["input"]);
+    CHECK(result == testcase["expected"]);
+
+    hackerrank::warmup::timeConversion(testcase["input"]);
+  }
+}
+
+TEST_CASE("time_conversion helper functions edge cases",
+          "[hackerrank] [helper] [warmup]") {
+
+  CHECK(hackerrank::warmup::firstN("", 10) == "");
+  CHECK(hackerrank::warmup::lastN("", 10) == "");
+
+  CHECK(hackerrank::warmup::firstN("", 0) == "");
+  CHECK(hackerrank::warmup::lastN("", 0) == "");
+}

src/tests/unit/lib/hackerrank/warmup/time_conversion.testcases.json

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+[
+  { "input": "12:01:00PM", "expected": "12:01:00" },
+  { "input": "12:01:00AM", "expected": "00:01:00" }
+]