traffic jam

jam.cc

#include <cassert>
#include <sstream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <list>
using std::endl;
using std::cout;

static float slowdown = 0.35;
static float spawn = 0.8;

static const int speed_max = 6;
static const int road_length = 120;
static int carid = 0;

struct Car {
    Car() {
	position = 0;
	speed = random()%speed_max;
	id = carid++;
    }

    int position;
    int speed;
    int id;
};

std::ostream &operator<<(std::ostream &os, const Car &car) {
    return os << "<car id=" << car.id << " speed=" << car.speed << " position=" << car.position << ">";
}

typedef std::list<Car> Cars;

void build_line(const Cars &cars, std::ostream &stream) {
    stream << "|";
    Cars::const_iterator iter = cars.begin();
    for (size_t current_position=0; current_position<road_length; current_position++) {
	if (iter==cars.end()) {
	    stream << " ";
	    continue;
	}
	
	assert(iter->position>=current_position);

	if (iter->position==current_position) {
	    stream << (iter->id % 10);
	    iter++;
	} else {
	    stream << " ";
	}
    }
    stream << "|" << endl;
}

void update(Cars &cars) {

    Cars::const_reverse_iterator iter_infront = cars.rend();
    for (Cars::reverse_iterator iter=cars.rbegin(); iter!=cars.rend(); iter++) {
	//cout << "--------------------" << endl << "updating " << *iter << endl;

	// remove cars that are too far
	if (iter->position>=road_length) {
	    assert(iter_infront==cars.rend());
	    assert(iter==cars.rbegin());
	    //cout << "removing " << *iter << endl;
	    cars.pop_back();
	    iter = cars.rbegin();
	    iter--;
	    continue;
	}

	// accelerate cars
	if (iter->speed>0 && random()<slowdown*RAND_MAX) {
	    iter->speed--;
	} else if (iter->speed<speed_max-1) {
	    iter->speed++;
	}

	// slow down in car blocks traffic
	if (iter_infront!=cars.rend() && iter->speed>=(iter_infront->position - iter->position)) {
	    iter->speed = iter_infront->position - iter->position - 1;
	    //cout << " infront "<< *iter_infront << endl;
	    assert(iter_infront->position>iter->position);
	}
	iter_infront = iter;

	iter->position += iter->speed;
	//cout << "updated  " << *iter << endl;
    }

    //cout << "moving cars" << endl;
    //for (Cars::reverse_iterator iter=cars.rbegin(); iter!=cars.rend(); iter++) {
    //    // update position
    //    iter->position += iter->speed;
    //}
}

int main(int argc,char * argv[])
{
    srandom(time(NULL));
    Cars cars;
    while (true) {
	if (cars.empty() || (!cars.empty() && cars.front().position!=0 && random()<spawn*RAND_MAX)) cars.push_front(Car());
	build_line(cars,cout);
	update(cars);
	usleep(25000);
    }
    return 0;
}