## C++, sort, wiggle_sort.cpp

``````/**
* @{
* \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 <algorithm>
#include <cassert>
#include <ctime>
#include <iostream>  /// for io operations
#include <vector>

/**
* @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
* 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;
}

/** @} */
``````