Monte Carlo

monte_carlo.cpp

#include <iostream>
#include <random>
#include <vector>
#include <math.h>
#include <sstream>

struct Vector {
  int x;
  int y;

  Vector& operator+=(Vector &o) {
    x += o.x;
    y += o.y;
    return *this;
  }
  
  int distance() {
    return abs(x) + abs(y);
  }

  const std::string print() {
    std::stringstream ss;
    ss << "(" << x << "," << y << ")";
    return ss.str();
  }
}; 

const Vector up    { 0,  1 };
const Vector down  { 0, -1 };
const Vector left  {-1,  0 };
const Vector right { 1,  0 };

Vector& choice() {
  std::vector<Vector> r_dir {
    up, down, left, right
  };

  return r_dir.at(rand() % 4);
}

Vector random_walk(int num_of_walks) {
  Vector xy{0, 0};
  for (int i = 0; i < num_of_walks; i++) {
    xy += choice();
  }
  return xy;
}

void test_2() {
  int number_of_walks = 20000;
  int walk_length = 30;

  for (int i = 1; i <= walk_length; i++) {
    int no_transport = 0;
    for (int j = 1; j <= number_of_walks; j++) {
      auto walk = random_walk(walk_length);
      if (walk.distance() <= 5) {
        no_transport += 1;
      }
    }

    float no_transport_percentage =  (float) no_transport / number_of_walks;
    std::cout << "Walk size: " << i << " " << " Percent " << 100*no_transport_percentage << std::endl; 
  }
}

void test_1() {
  int number_of_walks = 10;
  int walk_length = 25;

  for (int i = 1; i <= walk_length; i++) {
    auto walk = random_walk(number_of_walks);
    std::cout << walk.print() << " Distance from home: " << walk.distance() << std::endl;
  }
}

int main() {
  srand (time(NULL));

  test_1();
  test_2();

  return 0;
}