IIT Bombay
Data Structures and Algorithms
Prof. Ajit A. Diwan
Prof. Ganesh Ramakrishnan
Prof. Deepak B. Phatak
Department of Computer Science and Engineering
IIT Bombay
Session: Mumbai Vada-Pav Restaurant (Randomized simulation)
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
1
Random Numbers
IIT Bombay
• In the previous example, we simulated the arrival time of customers
using some ‘assumed’ time instances.
• In practice, such events will occur randomly
• When we throw a dice, we get a random value between 1 and 6
• We do not know, which will be next value
• On an average, we make 600 throws, we will get 100 of each value
• It is possible to ‘simulate’ such events by generating random numbers
• Called ‘pseudo’ random numbers, (generated by an algorithm)
• C++ provides functions to generate random numbers
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
2
Random Numbers
IIT Bombay
• Use ‘rand()’ to generate ‘uniformly distributed’ random numbers
• Returns a number from 0 to RAND_MAX
int r, dice, i;
for (i=0; i<10; i++) {
r = rand();
dice = r%6 + 1;
cout << dice << “ “;
}
2542625142
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
3
Random number generation
IIT Bombay
• We wish to generate a different sequence of numbers for each ‘run’
• Use ‘srand()’
• Initialize random number generator with a ‘seed’
• Different seed ensures a different sequence to be generated
• Use current time as seed for random generator
std::srand(std::time(0)); //use current time as seed
Output from two different executions:
4265516112
1213136566
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
4
Data Structures
IIT Bombay
Maintain information for food and customer arrival
• Structure 1: foodInfo
• Contains information of food item (ID, name, and rate)
• Structure 2: customerInfo
• Contains information of customer (ID and arrival time) that arrive and
stand in the queue to place an order
• Queue 1: customerQueue
• It is of type structure, ‘customerInfo’
• Contains information of customer
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
5
Data Structures
IIT Bombay
Maintain information of the orders placed and
The order that goes to the kitchen for preparation
• Structure 3: orders
• Contains information of the order placed by each customer (Token
ID, Items, Quantity, Cost, Number of items ordered, Total Cost to
be paid, and time for placing order)
• Structure 4: kitchen
• Contains the information stored in structure ‘order’, structure
‘customerInfo’, preparation and fulfilment time of order
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
6
Functions
IIT Bombay
• Function 1: loadMenu
• Passes information of one menu item to the function
‘setFoodItems’
• Function 2: setFoodItems
• Loads the menu of the restaurant
• Function 3: customerArrives
• Pushes the information of the customer on the queue
‘customerQueue’ (includes customer id and arrival time)
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
7
Functions
IIT Bombay
• Function 4: placeOrder
• Generates token ID
• Randomizes
• Number of items
• Item ID, Quantity of each item
• Calculates cost, and total cost
• Calculates time for placing order (based on randomization)
• Sends the order information to the kitchen
• Customer exits from the queue and waits at a table
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
8
Functions
IIT Bombay
• Function 5: orderGoesToKitchen
• Loads information of
• Order placed
• Customer
• Calculates
• Preparation time for the order
• Order fulfilment time
• Updates the ‘listInKitchen’ list
• Function 6: dispatchOrders
• Sorts the ‘listInKitchen’ list based on fulfilment time
• Dispatches orders
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
9
Program
IIT Bombay
struct customerInfo{
int custID;
int arrivalTime;
}; //End of structure
struct orders {
int tokenID;
int numberOfItems;
int item[20];
int qty[20];
int cost[20];
float totalCost;
int placingOrderTime;
}; //End of structure
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
struct foodInfo{
int foodID;
string foodName;
float rate;
}; //End of structure
struct kitchen {
struct orders order;
struct customerInfo cinfo;
int orderfulfilmentTime;
int preparationTime;
}; //End of structure
10
Program
IIT Bombay
class restaurant {
private:
static int custID, tokenID, foodIndex;
struct foodInfo food[100]; struct orders order;
list<kitchen> listInKitchen; queue<customerInfo> customerQueue;
public:
void loadMenu();
void setFoodItems(int id, string name, float amount);
void customerArrives(int time);
void placeOrder(); void orderGoesToKitchen();
void dispatchOrders();
}; //End of class
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
11
Program
IIT Bombay
int restaurant::custID = 0;
int restaurant::tokenID = 1000;
int restaurant::foodIndex = 0;
int generateRandom(int low, int high) {
//Return a random number between low and high
return ((rand() % (high-low+1)) + low);
} //End of function
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
12
Program
IIT Bombay
void restaurant::setFoodItems(int id, string name, float rate) {
food[foodIndex].foodID = id;
food[foodIndex].foodName = name;
food[foodIndex].rate = rate;
foodIndex++;
} //End of function
void restaurant::loadMenu() {
setFoodItems(1,"Vada Pav",10.0);
setFoodItems(2,"Uttappa",18.0);
…
setFoodItems(25,"Kothmir Wadi",26.0);
} //End of function
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
13
Program
IIT Bombay
void restaurant::customerArrives(int time) {
struct customerInfo cust;
cust.custID = ++custID;
cust.arrivalTime = time;
customerQueue.push(cust);
cout << "Customer: " << customerQueue.back().custID << ", "
<< customerQueue.back().arrivalTime << endl;
} //End of function
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
14
Program
IIT Bombay
void restaurant::placeOrder() {
int index=0, itemID, qty, i, low;
order.tokenID = ++tokenID;
int totalCost, ptime;
// Code for placing order
// Code for calculating placing order time
// Code to display order info of customer
} //End of function
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
15
Program
IIT Bombay
//Place order for numberOfItems items. where numberOfItems<=6
order.numberOfItems = generateRandom(1,6);
itemID = generateRandom(1,3);
index = generateRandom(1,3);
for (i=0;i<order.numberOfItems;i++) {
itemID = itemID + index;
qty = generateRandom(1,10); //Qty is from 1 to 10
order.item[i] = itemID;
order.qty[i] = qty;
order.cost[i] = food[itemID].rate * qty;
totalCost = totalCost + order.cost[i];
}
order.totalCost = totalCost;
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
16
Program
IIT Bombay
//Calculate placing order time
low = order.numberOfItems * 5;
ptime = generateRandom(low, low+15);
if (listInKitchen.empty())
order.placingOrderTime = ptime + customerQueue.front().arrivalTime;
else {
if (customerQueue.front().arrivalTime > listInKitchen.back().order.placingOrderTime)
order.placingOrderTime = ptime + customerQueue.front().arrivalTime;
else
order.placingOrderTime = ptime + listInKitchen.back().order.placingOrderTime;
} //End of else
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
17
Program
IIT Bombay
//Display order info of customer
cout << "Order placed for customer " << customerQueue.front().custID
<< " with token " << order.tokenID << " and timetaken is " << ptime << endl;
orderGoesToKitchen();
customerQueue.pop();
} //End of function placeOrder()
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
18
Program
IIT Bombay
void restaurant::orderGoesToKitchen() {
kitchen k;
int pTime;
k.order = order;
k.cinfo = customerQueue.front();
pTime = order.numberOfItems * 120;
k.preparationTime = generateRandom(pTime,pTime+60) ;
k.orderfulfilmentTime = k.preparationTime + order.placingOrderTime;
listInKitchen.push_back(k);
cout << "List in kitchen updated for token id: " << listInKitchen.back().order.tokenID
<< ", Preparation time: " << listInKitchen.back().preparationTime << endl << endl;
} //End of function
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
19
Program
IIT Bombay
bool compare(kitchen first, kitchen second) {
return (first.orderfulfilmentTime < second.orderfulfilmentTime);
} //End of function
void restaurant::dispatchOrders() {
listInKitchen.sort(compare);
int i;
while (!listInKitchen.empty()) {
cout << "Dispatched Token ID: " << listInKitchen.front().order.tokenID
<< " fulfilled at: " << listInKitchen.front().orderfulfilmentTime << endl;
listInKitchen.pop_front();
}
} //End of function
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
20
Program
IIT Bombay
int main() {
std::srand(std::time(0));
restaurant MVPRestaurant;
MVPRestaurant.loadMenu();
int i, custarrive=0;
for (i=1; i<=5; i++) {
custarrive = custarrive + generateRandom(1,20);
MVPRestaurant.customerArrives(custarrive);
} cout << endl;
for (i=1; i<=5; i++) {
MVPRestaurant.placeOrder();
} cout << endl;
MVPRestaurant.dispatchOrders();
return 0;
} //End of main()
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
21
IIT Bombay
Thank you
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay
22