fix: Intersection of two arrays (#1781)

* Create reverse_binary_tree.cpp

* Added documentation

Added Documentation for the level_order_traversal() function, and implemented a print() function to display the tree to STDOUT

* Added documentation

* Renamed tests to test

* Fixed issue with incorrect using statement

* updating DIRECTORY.md

* clang-format and clang-tidy fixes for fb86292d

* Added Test cases

* Update operations_on_datastructures/reverse_binary_tree.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update operations_on_datastructures/reverse_binary_tree.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update operations_on_datastructures/reverse_binary_tree.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update operations_on_datastructures/reverse_binary_tree.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update operations_on_datastructures/reverse_binary_tree.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Changed int to int64_t

* Updated documentation wording

* Reused code from union_of_two_arrays and modified for intersection

* Fixed bug and corrected test output

* Renamed file to better meet filename guidelines

* updating DIRECTORY.md

* clang-format and clang-tidy fixes for e653f77a

* Changed integer type from int64_t to int32_t

* Added reference to similar union_of_two_arrays file

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: Abhinn Mishra <49574460+mishraabhinn@users.noreply.github.com>

DIRECTORY.md

@@ -241,7 +241,7 @@
   * [Circular Queue Using Array](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/circular_queue_using_array.cpp)
   * [Get Size Of Linked List](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/get_size_of_linked_list.cpp)
   * [Inorder Successor Of Bst](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/inorder_successor_of_bst.cpp)
-  * [Intersection Of 2 Arrays](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/intersection_of_2_arrays.cpp)
+  * [Intersection Of Two Arrays](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/intersection_of_two_arrays.cpp)
   * [Reverse A Linked List Using Recusion](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/reverse_a_linked_list_using_recusion.cpp)
   * [Reverse Binary Tree](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/reverse_binary_tree.cpp)
   * [Selectionsortlinkedlist](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/operations_on_datastructures/selectionsortlinkedlist.cpp)

operations_on_datastructures/intersection_of_2_arrays.cpp

@@ -1,26 +0,0 @@
-#include <iostream>
-int main() {
-    int i, j, m, n;
-    cout << "Enter size of array 1:";
-    cin >> m;
-    cout << "Enter size of array 2:";
-    cin >> n;
-    int a[m];
-    int b[n];
-    cout << "Enter elements of array 1:";
-    for (i = 0; i < m; i++) cin >> a[i];
-    for (i = 0; i < n; i++) cin >> b[i];
-    i = 0;
-    j = 0;
-    while ((i < m) && (j < n)) {
-        if (a[i] < b[j])
-            i++;
-        else if (a[i] > b[j])
-            j++;
-        else {
-            cout << a[i++] << " ";
-            j++;
-        }
-    }
-    return 0;
-}

operations_on_datastructures/intersection_of_two_arrays.cpp

@@ -0,0 +1,203 @@
+/**
+ * @file
+ * @brief Implementation for the [Intersection of two sorted
+ * Arrays](https://en.wikipedia.org/wiki/Intersection_(set_theory))
+ * algorithm.
+ * @details The intersection of two arrays is the collection of all the elements
+ * that are common in both the first and second arrays. This implementation uses
+ * ordered arrays, and an algorithm to correctly order them and return the
+ * result as a new array (vector).
+ * @see union_of_two_arrays.cpp
+ * @author [Alvin](https://github.com/polarvoid)
+ */
+
+#include <algorithm>  /// for std::sort
+#include <cassert>    /// for assert
+#include <iostream>   /// for IO operations
+#include <vector>     /// for std::vector
+
+/**
+ * @namespace operations_on_datastructures
+ * @brief Operations on Data Structures
+ */
+namespace operations_on_datastructures {
+
+/**
+ * @brief Prints the values of a vector sequentially, ending with a newline
+ * character.
+ * @param array Reference to the array to be printed
+ * @returns void
+ */
+void print(const std::vector<int32_t> &array) {
+    for (int32_t i : array) {
+        std::cout << i << " ";  /// Print each value in the array
+    }
+    std::cout << "\n";  /// Print newline
+}
+
+/**
+ * @brief Gets the intersection of two sorted arrays, and returns them in a
+ * vector.
+ * @details An algorithm is used that compares the elements of the two vectors,
+ * incrementing the index of the smaller of the two. If the elements are the
+ * same, the element is appended to the result array to be returned.
+ * @param first A std::vector of sorted integer values
+ * @param second A std::vector of sorted integer values
+ * @returns A std::vector of the intersection of the two arrays, in ascending
+ * order
+ */
+std::vector<int32_t> get_intersection(const std::vector<int32_t> &first,
+                                      const std::vector<int32_t> &second) {
+    std::vector<int32_t> res;         ///< Vector to hold the intersection
+    size_t f_index = 0;               ///< Index for the first array
+    size_t s_index = 0;               ///< Index for the second array
+    size_t f_length = first.size();   ///< Length of first array
+    size_t s_length = second.size();  ///< Length of second array
+
+    while (f_index < f_length && s_index < s_length) {
+        if (first[f_index] < second[s_index]) {
+            f_index++;  ///< Increment index of second array
+        } else if (first[f_index] > second[s_index]) {
+            s_index++;  ///< Increment index of second array
+        } else {
+            if ((res.size() == 0) || (first[f_index] != res.back())) {
+                res.push_back(
+                    first[f_index]);  ///< Add the element if it is unique
+            }
+            f_index++;  ///< Increment index of first array
+            s_index++;  ///< Increment index of second array too
+        }
+    }
+    return res;
+}
+
+}  // namespace operations_on_datastructures
+
+/**
+ * @namespace tests
+ * @brief Testcases to check intersection of Two Arrays.
+ */
+namespace tests {
+using operations_on_datastructures::get_intersection;
+using operations_on_datastructures::print;
+/**
+ * @brief A Test to check an edge case (two empty arrays)
+ * @returns void
+ */
+void test1() {
+    std::cout << "TEST CASE 1\n";
+    std::cout << "Intialized a = {} b = {}\n";
+    std::cout << "Expected result: {}\n";
+    std::vector<int32_t> a = {};
+    std::vector<int32_t> b = {};
+    std::vector<int32_t> result = get_intersection(a, b);
+    assert(result == a);  ///< Check if result is empty
+    print(result);        ///< Should only print newline
+    std::cout << "TEST PASSED!\n\n";
+}
+/**
+ * @brief A Test to check an edge case (one empty array)
+ * @returns void
+ */
+void test2() {
+    std::cout << "TEST CASE 2\n";
+    std::cout << "Intialized a = {} b = {2, 3}\n";
+    std::cout << "Expected result: {}\n";
+    std::vector<int32_t> a = {};
+    std::vector<int32_t> b = {2, 3};
+    std::vector<int32_t> result = get_intersection(a, b);
+    assert(result == a);  ///< Check if result is equal to a
+    print(result);        ///< Should only print newline
+    std::cout << "TEST PASSED!\n\n";
+}
+/**
+ * @brief A Test to check correct functionality with a simple test case
+ * @returns void
+ */
+void test3() {
+    std::cout << "TEST CASE 3\n";
+    std::cout << "Intialized a = {4, 6} b = {3, 6}\n";
+    std::cout << "Expected result: {6}\n";
+    std::vector<int32_t> a = {4, 6};
+    std::vector<int32_t> b = {3, 6};
+    std::vector<int32_t> result = get_intersection(a, b);
+    std::vector<int32_t> expected = {6};
+    assert(result == expected);  ///< Check if result is correct
+    print(result);               ///< Should print 6
+    std::cout << "TEST PASSED!\n\n";
+}
+/**
+ * @brief A Test to check correct functionality with duplicate values
+ * @returns void
+ */
+void test4() {
+    std::cout << "TEST CASE 4\n";
+    std::cout << "Intialized a = {4, 6, 6, 6} b = {2, 4, 4, 6}\n";
+    std::cout << "Expected result: {4, 6}\n";
+    std::vector<int32_t> a = {4, 6, 6, 6};
+    std::vector<int32_t> b = {2, 4, 4, 6};
+    std::vector<int32_t> result = get_intersection(a, b);
+    std::vector<int32_t> expected = {4, 6};
+    assert(result == expected);  ///< Check if result is correct
+    print(result);               ///< Should print 4 6
+    std::cout << "TEST PASSED!\n\n";
+}
+/**
+ * @brief A Test to check correct functionality with a harder test case
+ * @returns void
+ */
+void test5() {
+    std::cout << "TEST CASE 5\n";
+    std::cout << "Intialized a = {1, 2, 3, 4, 6, 7, 9} b = {2, 3, 4, 5}\n";
+    std::cout << "Expected result: {2, 3, 4}\n";
+    std::vector<int32_t> a = {1, 2, 3, 4, 6, 7, 9};
+    std::vector<int32_t> b = {2, 3, 4, 5};
+    std::vector<int32_t> result = get_intersection(a, b);
+    std::vector<int32_t> expected = {2, 3, 4};
+    assert(result == expected);  ///< Check if result is correct
+    print(result);               ///< Should print 2 3 4
+    std::cout << "TEST PASSED!\n\n";
+}
+/**
+ * @brief A Test to check correct functionality with an array sorted using
+ * std::sort
+ * @returns void
+ */
+void test6() {
+    std::cout << "TEST CASE 6\n";
+    std::cout << "Intialized a = {1, 3, 3, 2, 5, 9, 4, 7, 3, 2} ";
+    std::cout << "b = {11, 3, 7, 8, 6}\n";
+    std::cout << "Expected result: {3, 7}\n";
+    std::vector<int32_t> a = {1, 3, 3, 2, 5, 9, 4, 7, 3, 2};
+    std::vector<int32_t> b = {11, 3, 7, 8, 6};
+    std::sort(a.begin(), a.end());  ///< Sort vector a
+    std::sort(b.begin(), b.end());  ///< Sort vector b
+    std::vector<int32_t> result = get_intersection(a, b);
+    std::vector<int32_t> expected = {3, 7};
+    assert(result == expected);  ///< Check if result is correct
+    print(result);               ///< Should print 3 7
+    std::cout << "TEST PASSED!\n\n";
+}
+}  // namespace tests
+
+/**
+ * @brief Function to test the correctness of get_intersection() function
+ * @returns void
+ */
+static void test() {
+    tests::test1();
+    tests::test2();
+    tests::test3();
+    tests::test4();
+    tests::test5();
+    tests::test6();
+}
+
+/**
+ * @brief main function
+ * @returns 0 on exit
+ */
+int main() {
+    test();  // run self-test implementations
+    return 0;
+}