feat: Add sorting/radix_sort2.cpp (#1268)

* radix_sort2.cpp

* Performed changes in radix_sort2.cpp

* Update sorting/radix_sort2.cpp

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

* Update sorting/radix_sort2.cpp

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

* updating DIRECTORY.md

* clang-format and clang-tidy fixes for e01027fa

* update radix_sort2.cpp

* Update sorting/radix_sort2.cpp

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

* Update sorting/radix_sort2.cpp

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

* Update sorting/radix_sort2.cpp

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

* Update sorting/radix_sort2.cpp

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

* update radix_sort2.cpp

* update radix_sort2.cpp

* update radix_sort2.cpp

* update radix_sort2.cpp

* update radix_sort2.cpp

* update radix_sort2.cpp

* update radix_sort2.cpp

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

DIRECTORY.md

@@ -266,6 +266,7 @@
   * [Quick Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/quick_sort.cpp)
   * [Quick Sort 3](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/quick_sort_3.cpp)
   * [Radix Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/radix_sort.cpp)
+  * [Radix Sort2](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/radix_sort2.cpp)
   * [Selection Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/selection_sort.cpp)
   * [Shell Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/shell_sort.cpp)
   * [Shell Sort2](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/shell_sort2.cpp)

sorting/radix_sort2.cpp

@@ -0,0 +1,118 @@
+/**
+ * @file
+ * @brief Algorithm of [Radix sort](https://en.wikipedia.org/wiki/Radix_sort)
+ * @author [Suyash Jaiswal](https://github.com/Suyashjaiswal)
+ * @details
+ * Sort the vector of unsigned integers using radix sort i.e. sorting digit by digit
+ * using [Counting Sort](https://en.wikipedia.org/wiki/Counting_sort) as subroutine.
+ * Running time of radix sort is O(d*(n+b)) where b is the base for representing
+ * numbers and d in the max digits in input integers and n is number of unsigned integers.
+ * consider example for n = 5, aray elements = 432,234,143,332,123
+ * sorting digit by digit
+ * sorting according to
+ * 1) 1st digit place
+ * => 432, 332, 143, 123, 234
+ *
+ * 2) 2nd digit place
+ * => 123, 432, 332, 234, 143
+ *
+ * 3) 3rd digit place
+ * => 123, 143, 234, 332, 432
+ *
+ * using count sort at each step, which is stable.
+ * stable => already sorted according to previous digits.
+*/
+
+/// header files
+#include <iostream>  /// for io operations
+#include <vector>    /// for std::vector
+#include <algorithm> /// for collection of functions
+#include <cassert>   /// for a macro called assert which can be used to verify assumptions
+
+/**
+ * @namespace sorting
+ * @brief Sorting algorithms
+ */
+namespace sorting {
+    /**
+    * @namespace radix_sort
+    * @brief Functions for [Radix sort](https://en.wikipedia.org/wiki/Radix_sort)
+    * algorithm
+    */
+    namespace radix_sort {
+        /**
+        * @brief Function to sort vector according to current digit using stable
+        * sorting.
+        * @param cur_digit - sort according to the cur_digit
+        * @param ar - vector to be sorted
+        * @returns std::vector sorted till ith digit
+        */
+        std::vector<uint64_t> step_ith(uint16_t cur_digit, const std::vector<uint64_t>& ar) {  // sorting according to current digit.
+            int n = ar.size();
+            std::vector<uint32_t> position(10, 0);
+            for (int i = 0; i < n; ++i) {
+                position[(ar[i] / cur_digit) %
+                         10]++;  // counting frequency of 0-9 at cur_digit.
+            }
+            int cur = 0;
+            for (int i = 0; i < 10; ++i) {
+                int a = position[i];
+                position[i] = cur;  // assingning starting position of 0-9.
+                cur += a;
+            }
+            std::vector<uint64_t> temp(n);
+            for (int i = 0; i < n; ++i) {
+                temp[position[(ar[i] / cur_digit) % 10]] =
+                    ar[i];  // storing ar[i] in ar[i]'s cur_digit expected position of
+                            // this step.
+                position[(ar[i] / cur_digit) %
+                         10]++;  // incrementing ar[i]'s cur_digit position by 1, as
+                                 // current place used by ar[i].
+            }
+            return temp;
+        }
+        /**
+        * @brief Function to sort vector digit by digit.
+        * @param ar - vector to be sorted
+        * @returns sorted vector
+        */
+        std::vector<uint64_t> radix(const std::vector<uint64_t>& ar) {
+            uint64_t max_ele = *max_element(ar.begin(), ar.end()); // returns the max element.
+            std::vector<uint64_t> temp = ar;
+            for (int i = 1; max_ele / i > 0;
+                 i *= 10) {  // loop breaks when i > max_ele because no further digits
+                             // left to makes changes in aray.
+                temp = step_ith(i,temp);
+            }
+            for (uint64_t i : temp) {
+                std::cout << i << " ";
+            }
+            std::cout << "\n";
+            return temp;
+        }
+    }  // namespace radix_sort
+}  // namespace sorting
+
+/**
+ * @brief Function to test the above algorithm
+ * @returns none
+ */
+static void tests() {
+    /// Test 1
+    std::vector<uint64_t> ar1 = {432, 234, 143, 332, 123};
+    ar1 = sorting::radix_sort::radix(ar1);
+    assert(std::is_sorted(ar1.begin(), ar1.end()));
+    /// Test 2
+    std::vector<uint64_t> ar2 = {213, 3214, 123, 111, 112, 142,
+                           133, 132,  32,  12,  113};
+    ar2 = sorting::radix_sort::radix(ar2);
+    assert(std::is_sorted(ar2.begin(), ar2.end()));
+}
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    tests();  // execute the tests
+    return 0;
+}