Solutions for problems 13, 16, 20 and 25

Signed-off-by: erick-alcachofa <erick@artichoke.dev>

problem-13/data/input

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problem-13/src/impl.hpp

@@ -0,0 +1,37 @@
+/*
+ * Project Euler Solutions - Core Implementation
+ * ---------------------------------------------
+ * Problem     : Large Sum
+ * URL         : https://projecteuler.net/problem=13
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+#pragma once
+
+#include <sstream>
+
+#include "bigint.hpp"
+
+static std::string Solve(std::stringstream in) {
+  std::string number;
+  BigInt ans{};
+
+  while (std::getline(in, number)) {
+    auto current = BigInt::fromString(number);
+
+    if (!current) {
+      return current.error();
+    }
+
+    ans = ans + current.value();
+  }
+
+  return ans.toString().substr(0, 10);
+}

problem-13/src/solution.cpp

@@ -0,0 +1,40 @@
+/*
+ * Project Euler Solutions - Main Translation Unit
+ * ------------------------------------------
+ * Problem     : Large Sum
+ * URL         : https://projecteuler.net/problem=13
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <iostream>
+#include <print>
+#include <sstream>
+#include <string>
+
+#include "timer.hpp"
+#include "impl.hpp"
+
+int main(int, char *[]) {
+  std::ios_base::sync_with_stdio(false),
+    std::cin.tie(nullptr),
+    std::cout.tie(nullptr);
+
+  std::string input = R"(@input@)";
+
+  decltype(Solve({})) ans = {};
+
+  {
+    Timer<Microseconds> timer;
+    ans = Solve(std::stringstream{input});
+  }
+
+  std::println("{}", ans);
+}

problem-13/src/test.cpp

@@ -0,0 +1,28 @@
+/*
+ * Project Euler Solutions - Test File
+ * ------------------------------------
+ * Problem     : Large Sum
+ * URL         : https://projecteuler.net/problem=13
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <gtest/gtest.h>
+
+#include <sstream>
+
+#include "impl.hpp"
+
+const char *input = R"(@example@)";
+
+TEST(Problem13, test) {
+  const auto ans = Solve(std::stringstream{input});
+  EXPECT_EQ(ans, "0");
+}

problem-16/data/example

@@ -0,0 +1 @@
+15

problem-16/data/input

@@ -0,0 +1 @@
+1000

problem-16/src/impl.hpp

@@ -0,0 +1,41 @@
+/*
+ * Project Euler Solutions - Core Implementation
+ * ---------------------------------------------
+ * Problem     : Power Digit Sum
+ * URL         : https://projecteuler.net/problem=166
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+#pragma once
+
+#include <cstdint>
+#include <sstream>
+#include <algorithm>
+#include <print>
+
+#include "types.hpp"
+#include "bigint.hpp"
+
+static int64_t Solve(std::stringstream in) {
+  i32 pow = 0;
+
+  in >> pow;
+
+  BigInt result = BigInt::fromInteger(1).value();
+  BigInt mult = BigInt::fromInteger(2).value();
+  
+  for (i32 i = 0; i < pow; ++i) {
+    result = result * mult;
+  }
+
+  return rg::fold_left(result.toString() |
+                    vw::transform([](char c) -> i64 { return c - '0'; }),
+                i64(0), std::plus<>());
+}

problem-16/src/solution.cpp

@@ -0,0 +1,40 @@
+/*
+ * Project Euler Solutions - Main Translation Unit
+ * ------------------------------------------
+ * Problem     : Power Digit Sum
+ * URL         : https://projecteuler.net/problem=166
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <iostream>
+#include <print>
+#include <sstream>
+#include <string>
+
+#include "timer.hpp"
+#include "impl.hpp"
+
+int main(int, char *[]) {
+  std::ios_base::sync_with_stdio(false),
+    std::cin.tie(nullptr),
+    std::cout.tie(nullptr);
+
+  std::string input = R"(@input@)";
+
+  decltype(Solve({})) ans = {};
+
+  {
+    Timer<Milliseconds> timer;
+    ans = Solve(std::stringstream{input});
+  }
+
+  std::println("{}", ans);
+}

problem-16/src/test.cpp

@@ -0,0 +1,28 @@
+/*
+ * Project Euler Solutions - Test File
+ * ------------------------------------
+ * Problem     : Power Digit Sum
+ * URL         : https://projecteuler.net/problem=166
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <gtest/gtest.h>
+
+#include <sstream>
+
+#include "impl.hpp"
+
+const char *input = R"(@example@)";
+
+TEST(Problem166, test) {
+  const auto ans = Solve(std::stringstream{input});
+  EXPECT_EQ(ans, 26);
+}

problem-20/data/example

@@ -0,0 +1 @@
+10

problem-20/data/input

@@ -0,0 +1 @@
+100

problem-20/src/impl.hpp

@@ -0,0 +1,43 @@
+/*
+ * Project Euler Solutions - Core Implementation
+ * ---------------------------------------------
+ * Problem     : Factorial Digit Sum
+ * URL         : https://projecteuler.net/problem=20
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+#pragma once
+
+#include <cstdint>
+#include <sstream>
+#include <algorithm>
+#include <print>
+
+#include "types.hpp"
+#include "bigint.hpp"
+
+static int64_t Solve(std::stringstream in) {
+  i32 n;
+
+  in >> n;
+
+  BigInt one = BigInt::fromInteger(1).value();
+  BigInt current = BigInt::fromInteger(1).value();
+  BigInt accumulator = BigInt::fromInteger(1).value();
+
+  for (i32 i = 0; i < n; ++i) {
+    accumulator = accumulator * current;
+    current = current + one;
+  }
+
+  return rg::fold_left(accumulator.toString() |
+                    vw::transform([](char c) -> i64 { return c - '0'; }),
+                i64(0), std::plus<>());
+}

problem-20/src/solution.cpp

@@ -0,0 +1,40 @@
+/*
+ * Project Euler Solutions - Main Translation Unit
+ * ------------------------------------------
+ * Problem     : Factorial Digit Sum
+ * URL         : https://projecteuler.net/problem=20
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <iostream>
+#include <print>
+#include <sstream>
+#include <string>
+
+#include "timer.hpp"
+#include "impl.hpp"
+
+int main(int, char *[]) {
+  std::ios_base::sync_with_stdio(false),
+    std::cin.tie(nullptr),
+    std::cout.tie(nullptr);
+
+  std::string input = R"(@input@)";
+
+  decltype(Solve({})) ans = {};
+
+  {
+    Timer<Microseconds> timer;
+    ans = Solve(std::stringstream{input});
+  }
+
+  std::println("{}", ans);
+}

problem-20/src/test.cpp

@@ -0,0 +1,28 @@
+/*
+ * Project Euler Solutions - Test File
+ * ------------------------------------
+ * Problem     : Factorial Digit Sum
+ * URL         : https://projecteuler.net/problem=20
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <gtest/gtest.h>
+
+#include <sstream>
+
+#include "impl.hpp"
+
+const char *input = R"(@example@)";
+
+TEST(Problem20, test) {
+  const auto ans = Solve(std::stringstream{input});
+  EXPECT_EQ(ans, 27);
+}

problem-25/data/example

@@ -0,0 +1 @@
+3

problem-25/data/input

@@ -0,0 +1 @@
+1000

problem-25/src/impl.hpp

@@ -0,0 +1,41 @@
+/*
+ * Project Euler Solutions - Core Implementation
+ * ---------------------------------------------
+ * Problem     : 25000-digit Fibonacci Number
+ * URL         : https://projecteuler.net/problem=25
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+#pragma once
+
+#include <print>
+#include <cstdint>
+#include <sstream>
+
+#include "types.hpp"
+#include "bigint.hpp"
+
+static int64_t Solve(std::stringstream in) {
+  i64 n = 0;
+
+  in >> n;
+
+  i64 iter = 2;
+
+  BigInt prev = BigInt::fromInteger(1).value();
+  BigInt curr = BigInt::fromInteger(1).value();
+
+  while (curr.toString().length() < n) {
+    ++iter;
+    prev = std::exchange(curr, prev + curr);
+  }
+
+  return iter;
+}

problem-25/src/solution.cpp

@@ -0,0 +1,40 @@
+/*
+ * Project Euler Solutions - Main Translation Unit
+ * ------------------------------------------
+ * Problem     : 25000-digit Fibonacci Number
+ * URL         : https://projecteuler.net/problem=25
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <iostream>
+#include <print>
+#include <sstream>
+#include <string>
+
+#include "timer.hpp"
+#include "impl.hpp"
+
+int main(int, char *[]) {
+  std::ios_base::sync_with_stdio(false),
+    std::cin.tie(nullptr),
+    std::cout.tie(nullptr);
+
+  std::string input = R"(@input@)";
+
+  decltype(Solve({})) ans = {};
+
+  {
+    Timer<Milliseconds> timer;
+    ans = Solve(std::stringstream{input});
+  }
+
+  std::println("{}", ans);
+}

problem-25/src/test.cpp

@@ -0,0 +1,28 @@
+/*
+ * Project Euler Solutions - Test File
+ * ------------------------------------
+ * Problem     : 25000-digit Fibonacci Number
+ * URL         : https://projecteuler.net/problem=25
+ *
+ * Author      : erick-alcachofa
+ * Created     : Tuesday, September 09 2025
+ *
+ * Notes:
+ * - 
+ *
+ * License     : GNU Affero General Public License v3.0 (AGPLv3)
+ *               https://www.gnu.org/licenses/agpl-3.0.html
+ */
+
+#include <gtest/gtest.h>
+
+#include <sstream>
+
+#include "impl.hpp"
+
+const char *input = R"(@example@)";
+
+TEST(Problem25, test) {
+  const auto ans = Solve(std::stringstream{input});
+  EXPECT_EQ(ans, 12);
+}