question01.cpp

//////Question 1 - basic STL
////
//////Task 1: improve fill_vector and vecOfVec.push_back performance - execution time can be reduced significantly, please explain the changes you made and how they improve
////// the application performance.
////
//////Task 2: Implement count_total_elements without using a "visible" for loop
////
//////Task 3: Implement merge_vec_of_vec 
////
////// Make sure you compile the code in "Release" configuration (e.g O2 optimization level).
////// Do not modify ELEMENT_COUNT and ITERATIONS and functions fill_vector,count_total_elements and merge_vec_of_vec function signatures  
//
#include <chrono>
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

constexpr size_t ELEMENT_COUNT = 1000 * 10000;
constexpr size_t ITERATIONS = 10;

std::vector<uint64_t> fill_vector(size_t elementCount) {
	//TODO: improve function performance
	/*Assignment is very efficient because it knows the size
	of the vector it is copying, and needs to call the memory manager only once vs to push back function that
	created a vector in (i) size and call (i) times to push back function */

	int* arr = new int[elementCount];
	for (int i = 0; i < elementCount; i++) {
		arr[i] = i;
	}
	std::vector<uint64_t> vec;
	vec.assign(arr, arr + elementCount);

	return vec;
}



/// This function should return the total elements in all of the vectors
//Implement count_total_elements without using a "visible" for loop

// help function to count total elements in a vector of vectors
size_t count_total_elements_rec(const std::vector<std::vector<uint64_t>>& vecOfVec, std::vector<std::vector<uint64_t>>::const_iterator it)
{
	if (it == vecOfVec.end())
		return 0;
	
	int size = (*it).size();
	auto it2 = it;
	return size + count_total_elements_rec(vecOfVec, ++it2);

}

// the acctual function to count total elements in a vector of vectors
size_t count_total_elements(const std::vector<std::vector<uint64_t>>& vecOfVec) {
	const std::vector<std::vector<uint64_t>>::const_iterator it = vecOfVec.begin();
	return count_total_elements_rec(vecOfVec, it);
}



/// This function should return a single vector that contain all of the elements of the vectors in vecOfVec
std::vector<uint64_t> merge_vec_of_vec(std::vector<std::vector<uint64_t>>& vecOfVec) {
	std::vector<uint64_t> mergedVec;

	for (int i = 0; i < vecOfVec.size(); i++)
	{
		mergedVec.insert(mergedVec.end(), vecOfVec[i].begin(), vecOfVec[i].end());
	}
	std::cout << std::endl;

	return mergedVec;

}

int main(int argc, char** argv)
{
	//Create vector of vectors
	std::vector<std::vector<uint64_t>> vecOfVec;
	auto start = std::chrono::steady_clock::now();
	for (size_t i = 0; i < ITERATIONS; i++) {
		std::vector<uint64_t> vec = fill_vector(ELEMENT_COUNT);
		//TODO: improve inserting performance
		vecOfVec.push_back(vec);
	}
	auto end = std::chrono::steady_clock::now();
	size_t averageIterationTimeUs = std::chrono::duration_cast<std::chrono::microseconds>(end - start).count() / ITERATIONS;
	std::cout << "Average iteration duration in microseconds: " << averageIterationTimeUs << std::endl;

	//Count elements
	size_t totalElements = count_total_elements(vecOfVec);
	std::cout << "Total elements in vecOfVec: " << totalElements << " " << std::endl;

	//Merge vector of vectors
	std::vector<uint64_t> mergedVec = merge_vec_of_vec(vecOfVec);
	std::cout << "Total elements in merged mergedVec: " << mergedVec.size() << std::endl;

	std::cout << "Press enter to exit" << std::endl;
	getchar();
	return 0;
}