From c74892191fd8cd7f814ce37c4d876ca8a5a46972 Mon Sep 17 00:00:00 2001
From: Suyash Jaiswal <suyash.18je0864@am.iitism.ac.in>
Date: Tue, 13 Oct 2020 00:11:30 +0530
Subject: [PATCH] radix_sort2.cpp

---
 sorting/radix_sort2.cpp | 115 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 sorting/radix_sort2.cpp

diff --git a/sorting/radix_sort2.cpp b/sorting/radix_sort2.cpp
new file mode 100644
index 000000000..45c719c44
--- /dev/null
+++ b/sorting/radix_sort2.cpp
@@ -0,0 +1,115 @@
+/**
+ * @file
+ * @brief Algorith of [Radix sort](https://en.wikipedia.org/wiki/Radix_sort)
+ * @author [Suyash Jaiswal](https://github.com/Suyashjaiswal)
+ * @details
+ * Sort the vector of integers using radix sort i.e. sorting digi by digit using count sort as subroutine.
+ * Running time of radix is O(d*(n+b)) where b is the base for representing numbers and d in the max digits in input inegers and n is number of integers.
+ * consider example for n = 5, array 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>
+#include <vector>
+/**
+ * @namespace sort
+ * @brief Functions for sorting a vector of integers.
+ */
+namespace sort
+{
+/**
+ * @namespace radix_sort
+ * @brief Functions for sorting a vector of integers using radix sort algorithm.
+ */
+    namespace radix_sort
+    {
+/**
+ * @brief Class to create a vector and sort it.
+ */
+    class radix{
+    public:
+    int n;
+    std::vector<int> ar;
+/**
+ * @brief Constructor that initializes the vector on creation.
+ * @param a vector to be sorted.
+ */
+    radix(std::vector<int>& a){
+        ar = a;
+        n = ar.size();
+    }
+    int get_max(){                                                      // returns the max element.
+        int mx;for(int i = mx = 0;i < n;i++)mx = std::max(mx,ar[i]);
+        return mx;
+    }
+    void show(){
+        for(int i = 0;i < n;i++)std::cout<<ar[i]<<" ";std::cout<<"\n";
+    }
+    void radix_sort();
+    void step_ith(int dig);
+};
+void radix :: step_ith(int cur_digit){                              // sorting according to current digit.
+    int 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;
+    }
+    int 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].
+    }
+    for(int i = 0;i < n;i++){
+        ar[i] = temp[i];
+    }
+}
+void radix :: radix_sort(){
+    int max_ele = get_max();
+    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 array.
+        step_ith(i);
+    }
+}
+}   // namespace radix_sort
+}   // namespace sort
+
+void test1(){
+    std::vector<int> ar = {432,234,143,332,123};
+    sort::radix_sort::radix obj(ar);
+    obj.radix_sort();
+    obj.show();
+}
+void test2(){
+    std::vector<int> ar = {213,3214,123,111,112,142,133,132,32,12,113};
+    sort::radix_sort::radix obj(ar);
+    obj.radix_sort();
+    obj.show();
+}
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main()
+{
+    test1();
+    test2();
+    return 0;
+}
\ No newline at end of file