#include <Rcpp.h>
#include <iostream>
#include <vector>

// This is a simple example of exporting a C++ function to R. You can
// source this function into an R session using the Rcpp::sourceCpp
// function (or via the Source button on the editor toolbar). Learn
// more about Rcpp at:
//
//   http://www.rcpp.org/
//   http://adv-r.had.co.nz/Rcpp.html
//   http://gallery.rcpp.org/
//

// [[Rcpp::export]]
int divisors_sum(int number) {
  std::vector<int> divisors;
  divisors.push_back(1);
  for (int i = 2; i <= number / 2; i++) {
    if (number % i == 0) {
      divisors.push_back(i);
    }
  }
  int sum = 0;
  for (size_t i = 0; i < divisors.size(); i++)
    sum += divisors[i];
  return sum;
}

// [[Rcpp::export]]
bool is_friendly_c(int x, int y) {
  return (divisors_sum(x) == y) && (divisors_sum(y) == x);
}

// You can include R code blocks in C++ files processed with sourceCpp
// (useful for testing and development). The R code will be automatically
// run after the compilation.
//

/*** R

divisors_r <- function(x) {
  y <- seq_len(x/2)
  y[ x%%y == 0 ]
}

is_friendly_r <- function(x, y) {
  answer <- (x == sum(divisors(y))) && (y == sum(divisors(x)))
  return(answer)
}
first = runif(1, 2, 500)
second = runif(1, 2, 500)

microbenchmark(
  is_friendly_r(first, second),
  is_friendly_c(first, second)
)

*/