From 168acd0e7705c285ec432240962f658a33170927 Mon Sep 17 00:00:00 2001
From: Alvin Philips <alvinphilips257@gmail.com>
Date: Sun, 24 Oct 2021 02:48:44 +0530
Subject: [PATCH] Rewrote array_left_rotation

---
 .../array_left_rotation.cpp                   | 120 +++++++++++++-----
 1 file changed, 91 insertions(+), 29 deletions(-)

diff --git a/operations_on_datastructures/array_left_rotation.cpp b/operations_on_datastructures/array_left_rotation.cpp
index 7b8f7f279..43b3baae3 100644
--- a/operations_on_datastructures/array_left_rotation.cpp
+++ b/operations_on_datastructures/array_left_rotation.cpp
@@ -1,31 +1,93 @@
-#include <iostream>
-using namespace std;
-int main() {
-    int n, k;
-    cout << "Enter size of array=\t";
-    cin >> n;
-    cout << "Enter Number of indeces u want to rotate the array to left=\t";
-    cin >> k;
-    int a[n];
-    cout << "Enter  elements of array=\t";
-    for (int i = 0; i < n; i++) {
-        cin >> a[i];
+/**
+ * @file
+ * @brief Implementation for the [Union of two sorted
+ * Arrays](https://en.wikipedia.org/wiki/Union_(set_theory))
+ * algorithm.
+ * @details The Union of two arrays is the collection of all the unique elements
+ * in the first array, combined with all of the unique elements of a second
+ * array. This implementation uses ordered arrays, and an algorithm to correctly
+ * order them and return the result as a new array (vector).
+ * @author [Alvin](https://github.com/polarvoid)
+ */
+
+#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
     }
-    int temp = 0;
-    for (int i = 0; i < k; i++) {
-        temp = a[0];
-        for (int j = 0; j < n; j++) {
-            if (j == n - 1) {
-                a[n - 1] = temp;
-            } else {
-                a[j] = a[j + 1];
-            }
-        }
-    }
-    cout << "Your rotated array is=\t";
-    for (int j = 0; j < n; j++) {
-        cout << a[j] << " ";
-    }
-    getchar();
-    return 0;
+    std::cout << "\n";  /// Print newline
 }
+
+/**
+ * @brief Shifts the given vector to the left by the shift amount and returns a
+ * new vector with the result. The original vector is not mutated.
+ * @details Shifts the values of the vector, by creating a new vector and adding
+ * values from the shift index to the end, then appending the rest of the
+ * elements from the start of the vector.
+ * @param array A reference to the input std::vector
+ * @param shift The amount to be shifted to the left
+ * @returns A std::vector with the shiftedd values
+ */
+std::vector<int32_t> shift_left(const std::vector<int32_t> &array,
+                                size_t shift) {
+    if (shift >= array.size()) {
+        return {};  ///< We got an invalid shift, return empty array
+    }
+    std::vector<int32_t> res(array.size());  ///< Result array
+    for (int i = shift; i < array.size(); i++) {
+        res.push_back(array[i]);  ///< Add values after the shift index
+    }
+    for (int i = 0; i < shift; i++) {
+        res.push_back(array[i]);  ///< Add the values from the start
+    }
+    return res;
+}
+
+}  // namespace operations_on_datastructures
+
+/**
+ * @namespace tests
+ * @brief Testcases to check Union of Two Arrays.
+ */
+namespace tests {
+using operations_on_datastructures::print;
+using operations_on_datastructures::shift_left;
+/**
+ * @brief A Test to check an edge case (two empty arrays)
+ * @returns void
+ */
+void test1() {
+    std::vector<int32_t> arr = {1, 2, 3, 4, 5};
+    print(shift_left(arr, 2));
+}
+}  // namespace tests
+
+/**
+ * @brief Function to test the correctness of get_union() function
+ * @returns void
+ */
+static void test() { tests::test1(); }
+
+/**
+ * @brief main function
+ * @returns 0 on exit
+ */
+int main() {
+    test();  // run self-test implementations
+    return 0;
+}
\ No newline at end of file