test/puzzles/training/median_stream.cpp

/*
VIM: let b:cf5build="clang -std=c++20 -O2 -pthread -lstdc++ -I. {SRC} -o {OUT}"
VIM: let b:cf5run="{OUT}"
VIM-: let b:cppflags=g:Iboost.g:Itbb
VIM-: let b:ldflags=g:Lboost.g:Ltbb
VIM-: let b:ldlibpath=g:Bboost.g:Btbb
*/
#include <iostream>
#include <exception>
#include <chrono>
#include <vector>
#include <algorithm>

/*
Median Stream
    You're given a list of n integers arr[0..(n-1)]. You must compute a list
    output[0..(n-1)] such that, for each index i (between 0 and n-1, inclusive),
    output[i] is equal to the median of the elements arr[0..i] (rounded down to
    the nearest integer).

    The median of a list of integers is defined as follows. If the integers were
    to be sorted, then:

    If there are an odd number of integers, then the median is equal to the
    middle integer in the sorted order.
    Otherwise, if there are an even number of integers, then the median is equal
    to the average of the two middle-most integers in the sorted order.

Input
    n is in the range [1, 1,000,000].
    Each value arr[i] is in the range [1, 1,000,000].
Output
    Return a list of n integers output[0..(n-1)], as described above.

Example 1
    n = 4
    arr = [5, 15, 1, 3]
    output = [5, 10, 5, 4]
    The median of [5] is 5, the median of [5, 15] is (5 + 15) / 2 = 10,
    the median of [5, 15, 1] is 5, and the median of [5, 15, 1, 3] is (3 + 5) / 2 = 4.

Example 2
    n = 2
    arr = [1, 2]
    output = [1, 1]
    The median of [1] is 1,
    the median of [1, 2] is (1 + 2) / 2 = 1.5 (which should be rounded down to 1).
*/

std::vector<int> findMedian(std::vector <int> arr) {
  // Write your code here
  std::vector<int> r;
  std::vector<int> l;

  for (size_t i = 0; i < arr.size(); ++i){
    l.push_back(arr[i]);
    std::push_heap(l.begin(), l.end());

    if (l.size() > ((i+1)/2+1)){
        std::pop_heap(l.begin(), l.end());
        l.resize(l.size()-1);
    }

    if ((i+1)%2){
      r.push_back(l[0]);
    } else if (l.size() == 2){
      r.push_back( (l[0]+l[1])/2 );
    } else {
      r.push_back( (l[0]+std::max(l[1],l[2]))/2 );
    }
  }
  return r;
}


// These are the tests we use to determine if the solution is correct.
// You can add your own at the bottom, but they are otherwise not editable!
void printIntegerVector(std::vector <int> array) {
  int size = array.size();
  std::cout << "[";
  for (int i = 0; i < size; i++) {
    if (i != 0) {
      std::cout << ", ";
    }
   std::cout << array[i];
  }
  std::cout << "]";
}

int test_case_number = 1;

void check(std::vector <int>& expected, std::vector <int>& output) {
  int expected_size = expected.size();
  int output_size = output.size();
  bool result = true;
  if (expected_size != output_size) {
    result = false;
  }
  for (int i = 0; i < std::min(expected_size, output_size); i++) {
    result &= (output[i] == expected[i]);
  }
  const char* rightTick = "PASS - ";
  const char* wrongTick = "FAIL - ";
  if (result) {
    std::cout << rightTick << "Test #" << test_case_number << "\n";
  }
  else {
    std::cout << wrongTick << "Test #" << test_case_number << ": Expected ";
    printIntegerVector(expected);
    std::cout << " Your output: ";
    printIntegerVector(output);
    std::cout << std::endl;
  }
  test_case_number++;
}

int main ( void )
{try{
    auto begin = std::chrono::high_resolution_clock::now();

    {
        std::vector <int> arr_1{5, 15, 1, 3};
        std::vector <int> expected_1{5, 10, 5, 4};
        std::vector <int> output_1 = findMedian(arr_1);
        check(expected_1, output_1);
    }{
        std::vector <int> arr_2{2, 4, 7, 1, 5, 3};
        std::vector <int> expected_2{2, 3, 4, 3, 4, 3};
        std::vector <int> output_2 = findMedian(arr_2);
        check(expected_2, output_2);
    }{
        std::vector <int> arr_2{2, 4, 7, 1, 5};
        std::vector <int> expected_2{2, 3, 4, 3, 4};
        std::vector <int> output_2 = findMedian(arr_2);
        check(expected_2, output_2);
    }{
        std::vector <int> arr_2{2, 4, 7, 1, 5, 3, 4};
        std::vector <int> expected_2{2, 3, 4, 3, 4, 3, 4 };
        std::vector <int> output_2 = findMedian(arr_2);
        check(expected_2, output_2);
    }

    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> seconds = end - begin;
    std::cout << "Time: " << seconds.count() << std::endl;
    return 0;
}
catch ( const std::exception& e )
{
    std::cerr << std::endl
            << "std::exception(\"" << e.what() << "\")." << std::endl;
    return 2;
}
catch ( ... )
{
    std::cerr  << std::endl
            << "unknown exception." << std::endl;
    return 1;
}}