Add merge sort

Author: rp-code9

Diff for: README.md

@@ -155,10 +155,10 @@ Princeton Algorithms [Part 1](https://www.coursera.org/learn/algorithms-part1/)
 * 8 Puzzle [Java](problems/matrices/8-puzzle/)
 
 ## Sorting
-* Insertion sort. (generic)  [Java](problems/sorting/Insertion.java)
+* Insertion sort (generic)  [Java](problems/sorting/Insertion.java)
 * Selection sort (generic)  [Java](problems/sorting/Selection.java)
 * Shell sort (generic)  [Java](problems/sorting/Shell.java)
-* Merge (generic)  [Java](problems/sorting/Merge.java)
+* Merge sort (generic)  [Java](problems/sorting/Merge.java) [C++](problems/sorting/MergeSort.cpp)
 * Bottom Up Merge (generic)  [Java](problems/sorting/MergeBU.java)
 * Quicksort (generic)  [Java](problems/sorting/Quick.java)
 * 3-way Quicksort (generic)  [Java](problems/sorting/Quick3Way.java)

Diff for: problems/sorting/MergeSort.cpp

@@ -0,0 +1,88 @@
+// Techie Delight https://www.techiedelight.com/merge-sort/
+
+#include <iostream>
+#include <vector>
+#include <cstdlib>
+#include <algorithm>
+
+void print(const std::vector<int>& nums)
+{
+    for (auto n : nums) {
+        std::cout << n << " ";
+    }
+}
+
+std::vector<int> generateRandomNumbers(const int length, const int min, const int max)
+{
+    std::vector<int> nums;
+    for (int i = 0; i < length; ++i) {
+        int x = min + (rand() % max - min + 1);
+        nums.push_back(x);
+    }
+    return nums;
+}
+
+void merge(std::vector<int>& nums, std::vector<int>& aux, int low, int mid, int high)
+{
+    int i = low;
+    int j = mid + 1;
+    int k = low;
+
+    while (i <= mid && j <= high) {
+        if (nums[i] <= nums[j]) {
+            aux[k++] = nums[i++];
+        } else {
+            aux[k++] = nums[j++];
+        }
+    }
+
+    while (i <= mid) {
+        aux[k++] = nums[i++];
+    }
+
+
+    while (j <= high) {
+        aux[k++] = nums[j++];
+    }
+
+    for (int i = low; i <= high; ++i) {
+        nums[i] = aux[i];
+    }
+}
+
+void mergesort(std::vector<int>& nums, std::vector<int>& aux, int low, int high)
+{
+    if (low == high) {
+        return;
+    }
+
+    int mid = low + (high - low) / 2;
+    mergesort(nums, aux, low, mid);
+    mergesort(nums, aux, mid + 1, high);
+    merge(nums, aux, low, mid, high);
+}
+
+void mergesort(std::vector<int>& nums)
+{
+    std::vector<int> aux(nums.size());
+    mergesort(nums, aux, 0, nums.size() - 1);
+}
+
+void test(std::vector<int>& nums)
+{
+    std::cout << "Numbers before sorting: ";
+    print(nums);
+    mergesort(nums);
+    std::cout << "\nNumbers after sorting: ";
+    print(nums);
+    std::cout << "\nIs sorted: " << std::boolalpha << std::is_sorted(nums.begin(), nums.end());
+    std::cout << "\n";
+}
+
+int main()
+{
+    std::vector<int> nums = generateRandomNumbers(20, -1000, 1000);
+    test(nums);
+
+    return 0;
+}