slide.cpp

#include <iostream>
#include <chrono>
#include <cassert>

using namespace std;

// Don't change this function!
void slide_ref(const int n, double* in, double* out) {
  auto start = chrono::steady_clock::now();
  out[0] = out[1] = out[n-2] = out[n-1] = 0;
  for(int i=2; i<n-2; i++) {
    out[i] = in[i-2] + in[i-1] + in[i] + in[i+1] + in[i+2];
  }
  auto end = chrono::steady_clock::now();
  auto diff = end - start;
  cout << chrono::duration <double, milli> (diff).count() << " ms\n";
}

// Please edit this function
void slide(const int n, double* in, double* out) {
  auto start = chrono::steady_clock::now();
  out[0] = out[1] = out[n-2] = out[n-1] = 0;
  for(int i=2; i<n-2; i++) {
    out[i] = in[i-2] + in[i-1] + in[i] + in[i+1] + in[i+2];
  }
  auto end = chrono::steady_clock::now();
  auto diff = end - start;
  cout << chrono::duration <double, milli> (diff).count() << " ms\n";
}

int main() {
  const int n = 100*1024*1024;
  double* in = new double[n];
  for(int i=0; i<n; i++)
    in[i] = i;
  double* out = new double[n];
  double* ref = new double[n];

  // compute the sliding average such that
  // out[i] = in[i-2] + in[i-1] + in[i] + in[i+1] + in[i+2]
  // let the first two and last two entries of the output be zero
  // out[0] = out[1] = out[n-2] = out[n-1] = 0;
  slide_ref(n,in,ref); // reference solution

  //write a faster version here!
  slide(n,in,out);

  for(int i=2; i<n-2; i++) {
    if(ref[i]!=out[i]) {
      cerr << "solution does not match at index " << i
           << "... exiting\n";
      return 1;
    }
  }

  return 0;
}