feat: add recursive inserstion sort

sorting/insertion_sort_recursive.cpp

@@ -0,0 +1,151 @@
+/**
+ * @file
+ * @brief Insertion Sort Algorithm
+ *
+ * @details
+ * Insertion sort is a simple sorting algorithm that builds the final
+ * sorted array one element at a time. It is much less efficient compared
+ * to other sorting algorithms like heap sort, merge sort, or quick sort.
+ * 
+ * However, it has several advantages:
+ * - Easy to implement.
+ * - Efficient for small data sets.
+ * - More efficient than other O(n²) algorithms like selection sort or bubble sort.
+ * - Stable: it does not change the relative order of elements with equal keys.
+ * 
+ * Insertion sort works similarly to how people sort playing cards in their hands.
+ * The algorithm iterates through the list and inserts each element into its correct 
+ * position in the sorted portion of the array.
+ *
+ * Example execution:
+ * 1. Start with the array [4, 3, 2, 5, 1].
+ * 2. Insert 3 in its correct position: [3, 4, 2, 5, 1].
+ * 3. Insert 2: [2, 3, 4, 5, 1].
+ * 4. Continue this until the array is sorted: [1, 2, 3, 4, 5].
+ */
+
+#include <algorithm>   ///< for std::is_sorted
+#include <cassert>     ///< for assert function in testing
+#include <iostream>    ///< for std::cout and std::endl
+#include <vector>      ///< for using std::vector
+
+/** 
+ * @namespace sorting
+ * @brief Contains sorting algorithms
+ */
+namespace sorting {
+
+/**
+ * @brief Insertion Sort Function
+ * 
+ * @tparam T Type of the array elements
+ * @param [in,out] arr Array to be sorted
+ * @param n Size of the array
+ */
+template <typename T>
+void insertionSort(T *arr, int n) {
+    for (int i = 1; i < n; i++) {
+        T temp = arr[i];
+        int j = i - 1;
+        while (j >= 0 && temp < arr[j]) {
+            arr[j + 1] = arr[j];
+            j--;
+        }
+        arr[j + 1] = temp;
+    }
+}
+
+/**
+ * @brief Insertion Sort for a vector
+ * 
+ * @tparam T Type of the vector elements
+ * @param [in,out] arr Pointer to the vector to be sorted
+ */
+template <typename T>
+void insertionSort(std::vector<T> *arr) {
+    size_t n = arr->size();
+
+    for (size_t i = 1; i < n; i++) {
+        T temp = arr->at(i);
+        int32_t j = i - 1;
+        while (j >= 0 && temp < arr->at(j)) {
+            arr->at(j + 1) = arr->at(j);
+            j--;
+        }
+        arr->at(j + 1) = temp;
+    }
+}
+
+}  // namespace sorting
+
+/**
+ * @brief Helper function to create a random array
+ * 
+ * @tparam T Type of the array elements
+ * @param arr Array to fill (must be pre-allocated)
+ * @param N Number of elements in the array
+ */
+template <typename T>
+static void create_random_array(T *arr, int N) {
+    while (N--) {
+        double r = (std::rand() % 10000 - 5000) / 100.f;
+        arr[N] = static_cast<T>(r);
+    }
+}
+
+/** 
+ * @brief Test Cases for the sorting algorithm 
+ */
+void tests() {
+    int arr1[10] = {78, 34, 35, 6, 34, 56, 3, 56, 2, 4};
+    std::cout << "Test 1... ";
+    sorting::insertionSort(arr1, 10);
+    assert(std::is_sorted(arr1, arr1 + 10));
+    std::cout << "passed" << std::endl;
+
+    int arr2[5] = {5, -3, 7, -2, 1};
+    std::cout << "Test 2... ";
+    sorting::insertionSort(arr2, 5);
+    assert(std::is_sorted(arr2, arr2 + 5));
+    std::cout << "passed" << std::endl;
+
+    float arr3[5] = {5.6, -3.1, -3.0, -2.1, 1.8};
+    std::cout << "Test 3... ";
+    sorting::insertionSort(arr3, 5);
+    assert(std::is_sorted(arr3, arr3 + 5));
+    std::cout << "passed" << std::endl;
+
+    std::vector<float> arr4({5.6, -3.1, -3.0, -2.1, 1.8});
+    std::cout << "Test 4... ";
+    sorting::insertionSort(&arr4);
+    assert(std::is_sorted(std::begin(arr4), std::end(arr4)));
+    std::cout << "passed" << std::endl;
+
+    int arr5[50];
+    std::cout << "Test 5... ";
+    create_random_array(arr5, 50);
+    sorting::insertionSort(arr5, 50);
+    assert(std::is_sorted(arr5, arr5 + 50));
+    std::cout << "passed" << std::endl;
+
+    float arr6[50];
+    std::cout << "Test 6... ";
+    create_random_array(arr6, 50);
+    sorting::insertionSort(arr6, 50);
+    assert(std::is_sorted(arr6, arr6 + 50));
+    std::cout << "passed" << std::endl;
+}
+
+/** 
+ * @brief Main function
+ * 
+ * Empty except for the call to `tests()`.
+ * 
+ * @return 0 Always returns 0.
+ */
+int main() {
+    /// Running predefined tests to test the algorithm
+    tests();
+
+    return 0;
+}