1. 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

2. Random Numbers
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

3. Random Numbers
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 << “ “; }
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

4. Random number generation
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:
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

5. Data Structures 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

6. Data Structures 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

7. Functions 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

8. Functions 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

9. Functions 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

10. Program struct customerInfo{ int custID; int arrivalTime;
}; //End of structure
struct foodInfo{
int foodID;
string foodName;
float rate;
}; //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
struct kitchen {
struct orders order;
struct customerInfo cinfo;
int orderfulfilmentTime;
int preparationTime;
}; //End of structure
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

11. Program 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

12. Program 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

13. Program
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

14. Program 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

15. Program 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

16. Program
//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

17. Program //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)
else
order.placingOrderTime = ptime + listInKitchen.back().order.placingOrderTime;
} //End of else
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

18. Program //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

19. Program 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

20. Program 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

21. Program
int main() {
std::srand(std::time(0));   restaurant MVPRestaurant; int i, custarrive=0;
MVPRestaurant.loadMenu();
for (i=1; i<=5; i++) {
custarrive = custarrive + generateRandom(1,20);
MVPRestaurant.customerArrives(custarrive);
} cout << endl;
MVPRestaurant.placeOrder();
MVPRestaurant.dispatchOrders();
return 0;
} //End of main()
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

22. Thank you
Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay