From bfbd694c8c437a56e04b86240bc33f4defe065c8 Mon Sep 17 00:00:00 2001
From: Legoeggolas <55898978+Legoeggolas@users.noreply.github.com>
Date: Sun, 28 Aug 2022 17:32:59 +0530
Subject: [PATCH] Add an implementation of merge sort.

---
 algorithms/C++/merge_sort/msort.cpp | 95 +++++++++++++++++++++++++++++
 algorithms/C++/merge_sort/msort.hpp | 20 ++++++
 2 files changed, 115 insertions(+)
 create mode 100644 algorithms/C++/merge_sort/msort.cpp
 create mode 100644 algorithms/C++/merge_sort/msort.hpp

diff --git a/algorithms/C++/merge_sort/msort.cpp b/algorithms/C++/merge_sort/msort.cpp
new file mode 100644
index 0000000..5c9fabe
--- /dev/null
+++ b/algorithms/C++/merge_sort/msort.cpp
@@ -0,0 +1,95 @@
+#include "msort.hpp"
+
+using vecIter = std::vector<int>::iterator;
+
+void merge(vecIter beginFirst,
+           vecIter endFirst,
+           vecIter beginSecond,
+           vecIter endSecond) {
+    auto const begin = beginFirst;
+
+    std::vector<int> temp(std::distance(beginFirst, endSecond));
+    auto it = temp.begin();
+
+    while (beginFirst != endFirst && beginSecond != endSecond) {
+        if (*beginFirst <= *beginSecond) {
+            *it = *beginFirst;
+            beginFirst++;
+        } else {
+            *it = *beginSecond;
+            beginSecond++;
+        }
+
+        it++;
+    }
+
+    while (beginFirst != endFirst) {
+        *it = *beginFirst;
+        it++;
+        beginFirst++;
+    }
+
+    while (beginSecond != endSecond) {
+        *it = *beginSecond;
+        it++;
+        beginSecond++;
+    }
+
+    it = temp.begin();
+    beginFirst = begin;
+    for (; beginFirst != endSecond; beginFirst++, it++) {
+        *beginFirst = *it;
+    }
+}
+
+void msort(vecIter begin, vecIter end) {
+    size_t len = std::distance(begin, end);
+    if (len <= 1) {
+        return;
+    }
+
+    auto mid = begin + (len / 2);
+
+    msort(begin, mid);
+    msort(mid, end);
+
+    merge(begin, mid, mid, end);
+}
+
+/*
+bool isSorted(vecIter begin, vecIter end) {
+    for (auto hare = begin + 1; hare != end; hare++, begin++) {
+        if (*hare < *begin) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
+int main() {
+    std::vector<int> vec(100000);
+
+    // First create an instance of an engine.
+    std::random_device rnd_device;
+    // Specify the engine and distribution.
+    std::mt19937 mersenne_engine{rnd_device()};  // Generates random integers
+    std::uniform_int_distribution<int> dist{1, 1024};
+
+    auto gen = [&dist, &mersenne_engine]() {
+        return dist(mersenne_engine);
+    };
+
+    std::generate(std::begin(vec), std::end(vec), gen);
+    assert(isSorted(vec.begin(), vec.end()) == false);
+
+    msort(vec.begin(), vec.end());
+
+    assert(isSorted(vec.begin(), vec.end()));
+
+    std::cout << "Done";
+
+    return 0;
+}
+*/
diff --git a/algorithms/C++/merge_sort/msort.hpp b/algorithms/C++/merge_sort/msort.hpp
new file mode 100644
index 0000000..24731ce
--- /dev/null
+++ b/algorithms/C++/merge_sort/msort.hpp
@@ -0,0 +1,20 @@
+#ifndef M_SORT_H
+#define M_SORT_H
+
+//#include <assert.h>
+
+#include <algorithm>
+//#include <iostream>
+#include <iterator>
+//#include <random>
+#include <vector>
+
+/**
+ * @brief Performs merge sort on a range defined by two iterators.
+ *
+ * @param begin The start of the range.
+ * @param end The end of the range.
+ */
+void msort(std::vector<int>::iterator begin, std::vector<int>::iterator end);
+
+#endif