IIT Bombay

Data Structures and AlgorithmsProf. Ajit A. Diwan

Prof. Ganesh RamakrishnanProf. Deepak B. Phatak

Department of Computer Science and EngineeringIIT Bombay

Session: Mumbai Vada-Pav Restaurant (Randomized simulation)

1Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay

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Random Numbers

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 2

• 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

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Random Numbers

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 3

• 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 << “ “;

}

2 5 4 2 6 2 5 1 4 2

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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:

4 2 6 5 5 1 6 1 1 2

1 2 1 3 1 3 6 5 6 6

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 4

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Data Structures

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 5

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

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Data Structures

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 6

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

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Functions

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 7

• 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)

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Functions

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 8

• 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

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Functions

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 9

• 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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 10

struct foodInfo{int foodID;string foodName;float rate;

}; //End of structure

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

struct kitchen {struct orders order;struct customerInfo cinfo;int orderfulfilmentTime;int preparationTime;

}; //End of structure

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 11

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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 12

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 highreturn ((rand() % (high-low+1)) + low);

} //End of function

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 13

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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 14

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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 15

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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 16

//Place order for numberOfItems items. where numberOfItems<=6order.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 10order.item[i] = itemID;order.qty[i] = qty;order.cost[i] = food[itemID].rate * qty; totalCost = totalCost + order.cost[i];

}order.totalCost = totalCost;

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 17

//Calculate placing order timelow = 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;

elseorder.placingOrderTime = ptime + listInKitchen.back().order.placingOrderTime;

} //End of else

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 18

//Display order info of customercout << "Order placed for customer " << customerQueue.front().custID

<< " with token " << order.tokenID << " and timetaken is " << ptime << endl;orderGoesToKitchen();customerQueue.pop();

} //End of function placeOrder()

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 19

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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 20

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

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Program

Ajit A. Diwan, Ganesh Ramakrishnan, and Deepak B. Phatak, IIT Bombay 21

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;for (i=1; i<=5; i++) {

MVPRestaurant.placeOrder();} cout << endl;MVPRestaurant.dispatchOrders();return 0;

} //End of main()

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Thank you

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