From e44943aadbbd727d93b23a8a578ac72d00d92527 Mon Sep 17 00:00:00 2001
From: Roshan Kanwar <roshan.18je0696@am.iitism.ac.in>
Date: Wed, 28 Oct 2020 22:51:49 +0530
Subject: [PATCH] feat: add wiggle sort algorithm (#1265)

* create wiggle_sort.cpp

* used array instead of vector

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* updating DIRECTORY.md

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* removed swap function and used std::swap

* update wiggle_sort.cpp

* update wiggle_sort.cpp

* Update wiggle_sort.cpp

* Update wiggle_sort.cpp

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
---
 DIRECTORY.md            |   1 +
 sorting/wiggle_sort.cpp | 136 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 sorting/wiggle_sort.cpp

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 1bdffd780..be27c717f 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -266,6 +266,7 @@
   * [Strand Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/strand_sort.cpp)
   * [Swap Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/swap_sort.cpp)
   * [Tim Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/tim_sort.cpp)
+  * [Wiggle Sort](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/sorting/wiggle_sort.cpp)
 
 ## Strings
   * [Brute Force String Searching](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/strings/brute_force_string_searching.cpp)
diff --git a/sorting/wiggle_sort.cpp b/sorting/wiggle_sort.cpp
new file mode 100644
index 000000000..4d75a22bb
--- /dev/null
+++ b/sorting/wiggle_sort.cpp
@@ -0,0 +1,136 @@
+/**
+ * \addtogroup sorting Sorting Algorithms
+ * @{
+ * \file
+ * \brief [Wiggle Sort Algorithm]
+ * (https://leetcode.com/problems/wiggle-sort-ii/) Implementation
+ *
+ * \author [Roshan Kanwar](http://github.com/roshan0708)
+ *
+ * \details
+ * Wiggle Sort sorts the array into a wave like array.
+ * An array ‘arr[0..n-1]’ is sorted in wave form,
+ * if arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4] >= …..
+ *
+ * \example
+ * arr = [1,1,5,6,1,4], after wiggle sort arr will become equal to [1,1,6,1,5,4]
+ * arr = [2,8,9,1,7], after wiggle sort arr will become equal to [8,2,9,1,7]
+ */
+
+#include <iostream>  /// for io operations
+#include <algorithm>
+#include <vector>
+#include <cassert>
+#include <ctime>
+
+/**
+ * @namespace sorting
+ * @brief Sorting algorithms
+ */
+namespace sorting {
+    /**
+    * @namespace wiggle_sort
+    * @brief Functions for [Wiggle Sort](https://leetcode.com/problems/wiggle-sort-ii/) algorithm
+    */
+    namespace wiggle_sort {
+
+        /**
+        *
+        * @brief Function used for sorting the elements in wave form.
+        * @details
+        * Checking whether the even indexed elements are greater than
+        * their adjacent odd elements.
+        * Traversing all even indexed elements of the input arr.
+        * If current element is smaller than the previous odd element, swap them.
+        * If current element is smaller than the next odd element, swap them.
+        *
+        * @param arr input array (unsorted elements)
+        *
+        */
+        template<typename T> // this allows to have vectors of ints, double, float, etc
+        std::vector<T> wiggleSort(const std::vector<T>& arr) {
+
+            uint32_t size = arr.size();
+
+            std::vector<T> out(arr); // create a copy of input vector. this way, the original input vector does not get modified. a sorted array is is returned.
+
+            for(int i = 0; i < size ; i +=2) {
+
+                if(i > 0 && out[i-1] > out[i]) {
+                    std::swap(out[i],out[i-1]); //swapping the two values
+                }
+
+                if(i < size - 1 && out[i] < out[i+1]) {
+                    std::swap(out[i],out[i+1]); //swapping the two values
+                }
+
+            }
+
+            return out; //returns the sorted vector
+
+        }
+    } // namespace wiggle_sort
+} // namespace sorting
+
+/**
+ *
+ * @brief Utility function used for printing the elements.
+ * Prints elements of the array after they're sorted using wiggle sort algorithm.
+ *
+ * @param arr array containing the sorted elements
+ *
+ */
+template<typename T>
+static void displayElements(const std::vector<T> &arr) {
+
+    uint32_t size = arr.size();
+
+    std::cout << "Sorted elements are as follows: ";
+
+    std::cout << "[";
+
+    for(int i = 0 ; i < size ; i++ ) {
+
+        std::cout << arr[i] ;
+        if(i != size - 1) {
+            std::cout << ", " ;
+        }
+
+    }
+
+    std::cout << "]"<<std::endl;
+
+}
+
+/**
+ * Test function
+ * @returns void
+ */
+static void test() {
+
+    std::srand(std::time(nullptr)); // initialize random number generator
+
+    std::vector<float> data1(100);
+    for (auto &d: data1) { // generate random numbers between -5.0 and 4.99
+        d = float(std::rand() % 1000 - 500) / 100.f;
+    }
+
+    std::vector<float> sorted = sorting::wiggle_sort::wiggleSort<float>(data1);
+
+    displayElements(sorted);
+
+    for(uint32_t j = 0; j < data1.size(); j+=2) {
+        assert(data1[j] <= data1[j+1] && data1[j+1] >= data1[j+2]); // check the validation condition
+    }
+
+    std::cout << "Test 1 passed\n";
+
+}
+
+/** Driver Code */
+int main() {
+    test();
+    return 0;
+}
+
+/** @} */