[feature] Gnome sort (#956)

* implement gnome sort algorithm

* change name as in contribute.md

* remove std and fixed style  on clang-format

* Delete GnomeSort.cpp

* style changes

* add documentation

* T template

* style changes

* style changes

* repeated error fix

* cout fixed

* fix gnome_sort

* add assertions'

* added random values test

* updating DIRECTORY.md

* clang-tidy fixes for 97161cf894dc547ad4b97bd1bc3af4e068a2c137

* fix initial index value

* add braces to one line for-loops

* fix function documentation
Co-authored-by: Nbeqakd <bgoga16@freeuni.edu.ge>
Co-authored-by: Nbeqakd <39763019+beqakd@users.noreply.github.com>
Co-authored-by: Ngithub-actions <${GITHUB_ACTOR}@users.noreply.github.com>

DIRECTORY.md

@@ -223,6 +223,7 @@
   * [Comb Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/comb_sort.cpp)
   * [Counting Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/counting_sort.cpp)
   * [Counting Sort String](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/counting_sort_string.cpp)
+  * [Gnome Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/gnome_sort.cpp)
   * [Heap Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/heap_sort.cpp)
   * [Insertion Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/insertion_sort.cpp)
   * [Library Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/library_sort.cpp)

sorting/gnome_sort.cpp

+/**
+ * @file
+ * @brief Implementation of [gnome
+ * sort](https://en.wikipedia.org/wiki/Gnome_sort) algorithm.
+ * @author [beqakd](https://github.com/beqakd)
+ * @author [Krishna Vedala](https://github.com/kvedala)
+ * @details
+ * Gnome sort algorithm is not the best one but it is widely used.
+ * The algorithm iteratively checks the order of pairs in the array. If they are
+ * on right order it moves to the next successive pair, otherwise it swaps
+ * elements. This operation is repeated until no more swaps are made thus
+ * indicating the values to be in ascending order.
+ *
+ * The time Complexity of the algorithm is \f$O(n^2)\f$ and in some cases it
+ * can be \f$O(n)\f$.
+ */
+
+#include <algorithm>  // for std::swap
+#include <array>      // for std::array
+#include <cassert>    // for assertions
+#include <iostream>   // for io operations
+
+/**
+ * @namespace sorting
+ * Sorting algorithms
+ */
+namespace sorting {
+/**
+ * This implementation is for a C-style array input that gets modified in place.
+ * @param [in,out] arr our array of elements.
+ * @param size size of given array
+ */
+template <typename T>
+void gnomeSort(T *arr, int size) {
+    // few easy cases
+    if (size <= 1) {
+        return;
+    }
+
+    int index = 0;  // initialize some variables.
+    while (index < size) {
+        // check for swap
+        if ((index == 0) || (arr[index] >= arr[index - 1])) {
+            index++;
+        } else {
+            std::swap(arr[index], arr[index - 1]);  // swap
+            index--;
+        }
+    }
+}
+
+/**
+ * This implementation is for a C++-style array input. The function argument is
+ * a pass-by-value and hence a copy of the array gets created which is then
+ * modified by the function and returned.
+ * @tparam T type of data variables in the array
+ * @tparam size size of the array
+ * @param [in] arr our array of elements.
+ * @return array with elements sorted
+ */
+template <typename T, size_t size>
+std::array<T, size> gnomeSort(std::array<T, size> arr) {
+    // few easy cases
+    if (size <= 1) {
+        return arr;
+    }
+
+    int index = 0;  // initialize loop index
+    while (index < size) {
+        // check for swap
+        if ((index == 0) || (arr[index] >= arr[index - 1])) {
+            index++;
+        } else {
+            std::swap(arr[index], arr[index - 1]);  // swap
+            index--;
+        }
+    }
+    return arr;
+}
+}  // namespace sorting
+
+/**
+ * Test function
+ */
+static void test() {
+    // Example 1. Creating array of int,
+    std::cout << "Test 1 - as a C-array...";
+    const int size = 6;
+    std::array<int, size> arr = {-22, 100, 150, 35, -10, 99};
+    sorting::gnomeSort(arr.data(),
+                       size);  // pass array data as a C-style array pointer
+    assert(std::is_sorted(std::begin(arr), std::end(arr)));
+    std::cout << " Passed\n";
+    for (int i = 0; i < size; i++) {
+        std::cout << arr[i] << ", ";
+    }
+    std::cout << std::endl;
+
+    // Example 2. Creating array of doubles.
+    std::cout << "\nTest 2 - as a std::array...";
+    std::array<double, size> double_arr = {-100.2, 10.2, 20.0, 9.0, 7.5, 7.2};
+    std::array<double, size> sorted_arr = sorting::gnomeSort(double_arr);
+    assert(std::is_sorted(std::begin(sorted_arr), std::end(sorted_arr)));
+    std::cout << " Passed\n";
+    for (int i = 0; i < size; i++) {
+        std::cout << double_arr[i] << ", ";
+    }
+    std::cout << std::endl;
+
+    // Example 3. Creating random array of float.
+    std::cout << "\nTest 3 - 200 random numbers as a std::array...";
+    const int size2 = 200;
+    std::array<float, size2> rand_arr{};
+
+    for (auto &a : rand_arr) {
+        // generate random numbers between -5.0 and 4.99
+        a = float(std::rand() % 1000 - 500) / 100.f;
+    }
+
+    std::array<float, size2> float_arr = sorting::gnomeSort(rand_arr);
+    assert(std::is_sorted(std::begin(float_arr), std::end(float_arr)));
+    std::cout << " Passed\n";
+    // for (int i = 0; i < size; i++) std::cout << double_arr[i] << ", ";
+    std::cout << std::endl;
+}
+
+/**
+ * Our main function with example of sort method.
+ */
+int main() {
+    test();
+    return 0;
+}