Sample questions for CS111 Midterm Exam 2

Transcription

1 Sample questions for CS111 Midterm Exam 2 1

2 Problem 1 [30 points] a) [15 points] Write a recursive method called power() that, given an integer n, returns 2 n (2 to the n th power). Recall that 2 0 = 1 and 2 1 = 2, 2 2 =(2*2)=4, 2 3 =2*2*2 = 8, etc. power() should not invoke any auxiliary methods. 2

3 b) [15 points] Write a recursive method called scream() that takes a StringList as a parameter and returns a StringList that has a capitalized last string, leaving all other strings intact. You may use the method touppercase() from the String contract (so you do not need to write touppercase()): public static String touppercase(string s) Returns the string s with all letters capitalized Examples: scream([ I, really, love, recursion ] Ë [ I, really, love, RECURSION ] scream([ ArE, you, crazy ]) Ë[ ArE, you, CRAZY ] 3

4 Problem 2 [40 points] [20 points] Write a method called skip such that it produces a row of bagels in every other cell in BuggleWorld. The method skip takes one integer parameter, n, that is the number of bagels that are dropped in a row. Your method must meet these three requirements: a) it must satisfy the invariant that the buggle s position and heading are not changed after invocation of the method b) it must be RECURSIVE c) it must not call any auxiliary methods (in other words, write all your code within the skip() method). This means you cannot use paintcell(). Here are some examples of invocations of skip with different parameters. skip(0) skip(1) skip(3) Important note: you do not need to worry about walls for this method. Assume a wall-free BuggleWorld. public void skip(int length) { // your code goes here 4

5 b) [20 points] Draw the final state of BuggleWorld after the invocation of skippile(4) (code for skippile() is given below). Assume your buggle starts in the usual starting location. Follow these conventions: Use a donut-shape to indicate a bagel, capital letters to indicate color, and a triangle to indicate the Buggle s final position and heading. public void skippile(int n) { if (n>=2) { skip(n); forward(); skip(n-1); backward(); forward(); left(); forward(); right(); skippile(n-1); left(); backward(); right(); backward();

6 Problem 3 [30 points] For questions a) and b) below, check as many boxes among those listed that are correct in the given context. It is possible that none of the responses are correct; it is also possible that all the responses are correct. a) [5 points] Assume you are given a method that returns an integer value called boomer : public int boomer () Returns an integer Check any of the boxes below that are acceptable expressions or statements in Java: i) int n = boomer(); ii) int count = boomer()+1; iii) boolean ans = boomer(); iv) boomer(boomer()); v) int tally = boomer() + boomer(); b) [5 points] Given the following lucky7() method below, check boxes corresponding to any of the expressions below that evaluate to true. public boolean lucky7(intlist list) { if (isempty(list)) { return false; else { if (head(list) == 7) { return true; else { return lucky7(tail(list)); i) lucky7([1,3,5,7]); ii) lucky7(lucky7([1,3,5,7])); iii) (lucky7([-7]) == true) iv) lucky7([7,7,7,7]); v) lucky7(7); 6

7 c) [5 points] Write a Java expression that will give the third (3 rd ) element in a given IntList, L. You can assume that the IntList L contains at least 3 elements in it. You may use the method abbreviations used in lecture, in other words, you may leave out the IntList.head() and simply write head(). d) [5 points] The Buggles have a professional basketball team! Using the information given below, write a boolean expression (not a method) that evaluates to true if a given Buggle can make the team. Team membership is entirely dependent on three variables: age (integer), height (integer) and brushdown (boolean). Membership on Buggle Basketball Team: A Buggle s age must be between 15 and 25 years old, inclusive (see height exception, below) A Buggle must be at least 10 inches tall. Any Buggle over 12 inches tall is automatically on the team, regardless of age and brushdown state. A Buggle s brushdown state should be false (see height exception, above) (and besides, who wants paint all over the basketball court?) 7

8 e) [10 points] Fill in the missing lines of code in the method hi() below. Assume that the turtle starts facing East with her brush down. hi() must meet the invariant that the turtle s heading and position are not changed after invocation of the method. Hint: this is not a recursive method. hi(25) produces the left picture below (the picture on the right is meant as a guide only): public void hi(int len) { // draw the h lt(90); fd(len*2); bd(len); rt(90); fd(len); rt(90); fd(len); // move to draw i pu(); lt(90); fd(len); pd(); // add your code here 8