From 68a75987e2a42e02650c7a0fd07d023bcba087f6 Mon Sep 17 00:00:00 2001
From: Jos van Goor <josvangoor@gmail.com>
Date: Thu, 1 Dec 2022 16:45:37 +0100
Subject: [PATCH] Euler 1-5

---
 project_euler/problem1.cc | 15 +++++++++++
 project_euler/problem2.cc | 31 ++++++++++++++++++++++
 project_euler/problem3.cc | 16 +++++++++++
 project_euler/problem4.cc | 19 +++++++++++++
 project_euler/problem5.cc | 24 +++++++++++++++++
 project_euler/sieve.h     | 56 +++++++++++++++++++++++++++++++++++++++
 6 files changed, 161 insertions(+)
 create mode 100644 project_euler/problem1.cc
 create mode 100644 project_euler/problem2.cc
 create mode 100644 project_euler/problem3.cc
 create mode 100644 project_euler/problem4.cc
 create mode 100644 project_euler/problem5.cc
 create mode 100644 project_euler/sieve.h

diff --git a/project_euler/problem1.cc b/project_euler/problem1.cc
new file mode 100644
index 0000000..e4d3dd5
--- /dev/null
+++ b/project_euler/problem1.cc
@@ -0,0 +1,15 @@
+#include <cstdint>
+#include <fmt/format.h>
+
+int main()
+{
+    std::int64_t result = 0;
+
+    for (std::int64_t value = 3; value < 1000; value += 3)
+        result += value;
+
+    for (std::int64_t value = 5; value < 1000; value += 5)
+        result += value % 3 == 0 ? 0 : value;
+
+    fmt::print("Result: {}\n", result);
+}
\ No newline at end of file
diff --git a/project_euler/problem2.cc b/project_euler/problem2.cc
new file mode 100644
index 0000000..873df57
--- /dev/null
+++ b/project_euler/problem2.cc
@@ -0,0 +1,31 @@
+#include <cstdint>
+#include <fmt/format.h>
+
+std::int64_t fibonacci()
+{
+    static std::int64_t first = 1;
+    static std::int64_t second = 2;
+
+    std::int64_t result = first + second;
+    std::swap(first, second);
+    second = result;
+
+    return result;
+}
+
+int main()
+{
+    std::int64_t result = 2;
+
+    while (true)
+    {
+        std::int64_t value = fibonacci();
+        if (value >= 4'000'000)
+            break;
+        
+        if (value % 2 == 0)
+            result += value;
+    }
+
+    fmt::print("Result: {}\n", result);
+}
\ No newline at end of file
diff --git a/project_euler/problem3.cc b/project_euler/problem3.cc
new file mode 100644
index 0000000..fe8310f
--- /dev/null
+++ b/project_euler/problem3.cc
@@ -0,0 +1,16 @@
+#include <cstdint>
+#include <fmt/format.h>
+
+#include "sieve.h"
+
+int main()
+{   
+    std::uint64_t input = 600'851'475'143;
+    auto sieve = std::make_unique<Sieve<1'000'000>>();
+    
+    for (auto value = static_cast<std::uint64_t>(std::sqrt(input)); value--; )
+    {
+        if (sieve->is_prime(value) && input % value == 0)
+            fmt::print("Result: {}\n", value);
+    }
+}
\ No newline at end of file
diff --git a/project_euler/problem4.cc b/project_euler/problem4.cc
new file mode 100644
index 0000000..6896162
--- /dev/null
+++ b/project_euler/problem4.cc
@@ -0,0 +1,19 @@
+#include <cstdint>
+#include <fmt/format.h>
+
+int main()
+{
+    std::uint64_t max = 0;
+
+    for (std::size_t a = 999; a > 99; a--)
+    {
+        for (std::size_t b = 999; b > 99; b--)
+        {
+            std::string number = std::to_string(a * b);
+            if (std::equal(number.begin(), number.end(), number.rbegin()))
+                max = std::max(max, a * b);
+        }
+    }
+
+    fmt::print("Result: {}\n", max);
+}
diff --git a/project_euler/problem5.cc b/project_euler/problem5.cc
new file mode 100644
index 0000000..bdc6608
--- /dev/null
+++ b/project_euler/problem5.cc
@@ -0,0 +1,24 @@
+#include <cstdint>
+#include <fmt/format.h>
+
+int main()
+{
+    for (std::int64_t value = 40; ; value += 20)
+    {
+        bool valid = true;
+        for (std::size_t divisor = 2; divisor <= 20; ++divisor)
+        {
+            if (value % divisor != 0)
+            {
+                valid = false;
+                break;
+            }
+        }
+
+        if (valid)
+        {
+            fmt::print("Result: {}\n", value);
+            return 0;
+        }
+    }
+}
\ No newline at end of file
diff --git a/project_euler/sieve.h b/project_euler/sieve.h
new file mode 100644
index 0000000..50cee17
--- /dev/null
+++ b/project_euler/sieve.h
@@ -0,0 +1,56 @@
+#ifndef SIEVE_H
+#define SIEVE_H
+
+#include <array>
+#include <concepts>
+#include <cstdint>
+
+template <std::uint64_t Max>
+class Sieve
+{
+    std::array<bool, Max> _primes{};
+
+    public:
+        Sieve()
+        {
+            for (bool& primeness : _primes)
+                primeness = true;
+
+            for (std::size_t idx = 3; idx < static_cast<std::size_t>(std::sqrt(Max)); idx += 2)
+            {
+                if (!_primes[index(idx)])
+                    continue;
+
+                for (std::size_t value = (2 * idx); value < Max; value += idx)
+                {
+                    if (value % 2 == 0)
+                        continue;
+                    _primes[index(value)] = false;
+                }
+            }
+        }
+
+        bool is_prime(std::uint64_t number) const noexcept
+        {
+            if (number == 2)
+                return true;
+            
+            if ((number == 0) || (number >= Max) || (number % 2 == 0))
+                return false;
+
+            return _primes[index(number)];
+        }
+
+        std::uint64_t size() const noexcept
+        {
+            return Max;
+        }
+
+    private:
+        std::size_t index(std::int64_t number) const noexcept
+        {
+            return (number - 1) / 2;
+        }
+};
+
+#endif
\ No newline at end of file