HOMEWORK #4 Solution

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Be sure to include your name at the beginning of each file! Assignment 4 include a programming portion and a written part. The programming portion must compile and consist of a single file ( hw04.cpp). The written portion should consist of a single file (hw04written) in a .pdf format. Be sure to include your name at the beginning of each file! You must hand in the file via NYU Classes.

Programming Part: Some of the recursion programming exercises could easily be written without recur- sion, but in order to practice recursion, you will write them recursively.

1. Create a menu for the user to access the data created in programming problem 1 in assignment 3B1

In the interactive phase, the program will repeatedly prompt the user to take any one of the following actions:

(a) Print out the information about all the train stops on a specific route; if no route is found, you should print out a message informing the user.

(b) Print out the information about a specific train stop; if no train stop is found, you should print out a message informing the user.

(c) Print out all the train stops within a certain distance, where the user enters the geographical coor- dinates. If no stop is found within the distance, print out a message informing the user.

(d) quit

To perform these operations you will define one generic function template2 and four functors.

Write a generic function template called perform if that takes four parameters: two iterators, itrStart, itrEnd, and two functors, pred and op. The two iterators should have have the capability of forward iterators. Both functors will have the overloaded operator() that takes one argument. The functor pred’s overloaded operator() returns a boolean value; the functor op’s overloaded operator() does not return any value. The function will apply pred’s overloaded operator() to each item in the range [itrStart, itrEnd). If pred’s overloaded operator() returns true, the other functor op’s overloaded operator() is then applied to the item, e.g.

if ( pred( *itr ) )

{

op(*itr);

how_many++;

}

The return value of the generic function template perform if is an int which returns the number of items for which the functor pred returned true.

The four functors you will write are:

(a) Write a functor called isStopOnRoute that has a private member variable called route of type char.

The constructor takes a single parameter of type char which it uses to initialize the variable route. It also contains an overloaded operator() that takes a single parameter of type trainStopData; the operator returns true if the train stop is on the route.3

(b) Write a functor called isSubwayStop that has a private member variable called stopId of type string. The constructor takes a single parameter of type string which it uses to initialize the variable stopId. It also contains an overloaded operator() that takes a single parameter of type trainStopData; the operator returns true if the train stop has an id which is the same as stopid.

(c) Write a functor called isSubwayStopNearX that has three private member variables called longitude, latitude, and d of type double. The constructor takes three parameters of type double which it uses to initialize the private member variables. It also contains an overloaded operator() that takes a single parameter of type trainStopData; the operator returns true if the distance between the train station location and the value of the functors private member variables, longitude and latitude, is at most d. The distance between two points on a sphere is computed using the haversine formula. The code to compute this formula is on NYU Classes in a file called haversine.txt.4

(d) Write a functor called printTrainStopInfo. This class contains a single method, an overloaded operator(), that takes a single parameter of type trainStopData that prints out the train stop information.

2. Write a recursive function called GCD that takes as arguments two integers a, b, and returns the greatest common divisor of the two numbers by using the following rule.

GCD(a,b) is a if b == 0

GCD(a,b) is GCD(b,a) if a < b

Otherwise GCD(a,b) is GCD(b, a mod b)

3. Write a program that sums the items in a vector using a divide and conquer algorithm. Create a driver function to call the recursive function; the driver function returns the value returned by the recursive function.

The driver function takes one parameter of type vector<int> and returns an int. The prototype for driver function is:

int sumVector( const vector<int> & a) // driver program

The recursive function’s parameters should be iterators that signify a range [left, right). Remember to include a base case.

If a contains {−9, 12, 8} then the function returns 11. (i.e. 11 = −9 + 12 + 8.) If a contains {3} then the function returns 3.

If a contains {−21, 31, 14, 1, −20} then the function returns 5. (i.e. 5 = −21 + 31 + 14 + 1 20.)

3 The train stop route is the first letter of the train stop id. For example, train stop id 202 is on route 2, and train stop id B20 is on route B.

4 You might need to add #define USE MATH DEFINES.

The function should: Divide the vector in half. Recurse on the left hand side. Recurse on the right hand side. Return the sum of both sides.

This function should not have any loops.

4. (Extra Credit Problem) Problem 8.25 from the older Weiss book: Write the routine with the declaration:

void permute( const string & str );

that prints all the permutations of the characters in the str. If str is “abc”. then the strings output are

abc, acb, bac, bca, cab, and cba. Use recursion.5

Written Part:

1. In programming part 1 of this assignment, you are asked to write a generic function template called

perform_if.

Write the pseudo code for the three to six main steps need to implement perform_if.

Write the preconditions and postconditions of the function.

Using Big-Oh notation, what is the running time of this generic function template?

2. Show the recursion tree and the runtime for:

(a) programming question 2 when a = 30 and b = 42. In your recursion tree show the parameters a and

b.

(b) programming question 3 when a = {1, 2, 3, 4}. In your recursion tree show the items in the range

[lef t, right).

3. Given the following code snippet:

vector<int> a {1,2,3,4, …, n}; // vector, a, has n items vector<int>::iterator itrStart;

vector<int>::iterator itrMid;

vector<int>::iterator itrEnd;

Assign values to the iterators, itrStart, itrMid, itrEnd, so that: (a) [itrStart, itrMid) refers to the range 1,2, 3, …, n/2

(b) [itrMid, itrEnd) refers to the range n/2+1,n/2+2, …, n

4. (a) What is printed by the following function call: myRecFunc(4).

(b) What is the running time of myRecFunc(n).

void myRecFunc(int n)

{

cout << n << “: “; if (n < 1) return; myRecFunc(n/2); myRecFunc(n/2);

for (int i = 1; i < n; ++i)

cout << “*”;

cout << endl;

}

5. For this recursive Fibonacci function, fib, how many function calls are made if n=3; how about if n=4?

Using the the number of function calls fib made when when n=3 and when n= 4, compute how many function calls are made when n=5. Show your work.

int fib( int n )

{

if( n <= 1 )

return 1;

else

return fib( n 1 ) + fib( n 2 );

}