AP® COMPUTER SCIENCE A

AP

® COMPUTER SCIENCE A

2014

GENERAL SCORING GUIDELINES

Apply

the

question

assessment

rubric first,

which

always

takes

precedence

. Penalty

points

can

only

be

deducted

in

a

part

of

the

question

that

has

earned

credit

via

the

question

rubric.

No

part

of a question

(a, b,

c)

may

have

a negative

point

total. A given penalty

can

be

assessed

only

once

for

a question,

even

if

it

occurs multiple

times

or

in

multiple

parts

of

that

question.

1-Point

Pena

l

ty

(w)

E

xtraneous

code

that

causes

side

effect

(e

.g.,

writing

to

output,

failure

to compile)

(x)

Local variables

used

but

none declared

(y)

D

estruction

of

persistent

data

(e

.g

.,

changing

value

referenced

by

parameter)

(z)

Void

method

or constructor

that

returns a value

No

Penalty

o

E

xtraneous

code

with

no

side

effect

(e

.g.,

precondition

check,

no

-op)

o

Spelling/case

discrepancies

where

there

is no ambiguity*

o

Local variable

not

declared

provided other variables are declared

in

some

part

o

private

or

public

qualifier

on

a local variable

o

Missing

public

qualifier

on

class or constructor

header

o

Keyword

used

as

an

identifier

o

Common

mathematical

symbols

used

for operators

(x

•

~

<>

*)

o

[]

vs.

()

vs.

<>

o =

instead

of

==

and

vice

versa

o

Array/collection

access

confusion

[

] get

o

length/size

confusion

for

array,

String

List

,

or

ArrayList

,

with

or

without

( )

o

E

xtraneous

[]

when

referencing entire array

o

[i,j]

instead

of

[i][j]

o

E

xtraneous

size

in

array declaration,

e.g

.,

int[size

]

nums = new int[size];

o

Missing

;

provided majority

are

present

and

indentation

clearly conveys

intent

o

Missing

{ }

where

indentation

clearly conveys

intent

and

{ }

are

used

elsewhere

o

Missing

( )

on

parameter

-less

method

or constructor invocations

o

Missing

( )

around

if

or

while

conditions

*Spelling

and

case discrepancies

for

identifiers

fall

under

the "No

Penalty"

category

only

if

the

correction

can

be

un

a

mb

i

guously

inferred

from

context;

for

example,

"

A

rayList

"

instead

of

"

A

rrayList

".

As

a counterexample,

note

that

if

the

code declares

"

B

ug bug;

",

then

uses

"

B

ug.move()

"

instead

of

"

b

ug.move()

",

the

context

does

not

allow

for

the

reader

to assume the

object

instead

of

the

class.

©

2014

The

College Board.

Visit

the

College Board

on

the

Web: www.collegeboard.org.

2014

SCORING GUIDELINES

Question

1:

Word

Scramble

Part

(a)

s

c

rambleWord

5

points

!

AP

® COMPUTER SCIENCE A

Intent:

Scramble a

word

by

swapping

all

letter

pairs

that

begin

with

A

+1

A

ccesses

all

letters in

word,

left to right

(no

bounds

errors)

+1

Identifies

at

least

one letter pair

consisting

of "A"

fo

ll

owed

by

non

-"A"

+1

Reverses identified pair

in

constructing

result

string

+1

C

onstructs

correct result

string

(P

oint

lost

if

any

letters

swapped

more

than once,

minor

loop

bounds

errors

ok

)

+1

R

eturns

constructed

string

!Part

(b)

s

crambleOrRemove

4

points

Intent:

M

odify

list

by

rep

l

acing

each

word

with

scramb

l

ed

version

and

removing

any

word

unchanged

by

scrambling

+ 1 A

ccesses

a

ll

words

in

wordList

(no

bo

u

nds

errors)

+ 1 Calls

scrambleWord

with

a word from

the

list

as

parameter

+ 1 Identifies words u

nchanged

by

scrambling

+1

On exit: L

ist

includes all

and

only words

that

have

been

changed

by scrambling

once

,

in

their original relative order

(minor

loop

bounds

errors ok)

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th

e Colle

ge

Board

on

the

Web:

www

.collegeboard.org.

2014

CANONICAL SOLUTIONS

Question

1:

Word

Scramble

Part

(a):

p

u

b

l

ic static String scrambleWord(String word){

int current = 0;

String result="";

while (current < word.length()-1){

if (word.substring(current,current+1).equals("A") &&

!word.substring(current+1,current+2).equals("A")){

result += word.substring(current+1,current+2);

result += "A";

current += 2;

}

else {

result += word.substring(current,current+1);

current++;

}

if (current < word.length()){

result += word.substring(current);

}

return result;

}

Part

(b):

p

u

b

lic static void scrambleOrRemove(List<String> wordList){

int index = 0;

while (index < wordList.size()){

String word=wordList.get(index);

String scrambled=scrambleWord(word);

if (word.equals(scrambled)){

wordList.remove(index);

}

else {

wordList.set(index,scrambled);

index++;

}

AP®

COMPUTER SCIENCE A

Th

ese

c a

nonic

al

so

lutions

serve

an

exp

ository role,

depic

ti

ng

genera

l

approaches

to

solution.

Each

re

fl

ects

on

ly

one

in

st

a

nce

from

the

infinite

se

t of

va

li

d

so

luti

ons

.

The

so

luti

ons

are

pr

ese

nt

ed

in a

codmg

style

chose

n to

enha

n

ce

r

ea

d

abi

lity

and

fa

ci

lit

ate

u

nde

rstan

di

ng

.

©

2014

The

College Board.

Visit

the

College Board

on

the

Web

www

.c o

ll

eg

e

bo

ar

d .o

rg

.

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2014 SCORING COMMENTARY

AP

Question 1

Overview

This question asked the students to write two static methods for an unnamed class which had no instance

variables. The question involved using methods of the String class (to get individual letters of the

String and to build a new String) and methods of the List interface (to access elements of the

List and to modify an existing List). In part (a), the students were required to implement a static

method called scrambleWord to scramble a String parameter (word) by reversing pairs of

adjacent letters of word whenever the pair consisted of "A" followed by a letter that was not "A". The

students needed to access all letters in word from left to right, identifying the pairs of letters to be

swapped. The identified pair could be reversed by rebuilding word or by constructing a new result

String. All letters of word that were not involved in reversals were to be in their original positions in

the result String, which was then returned by the method. In part (b), the students were required to

implement a static method called scrambleOrRemove. The method had a List parameter

(wordList) in which each element was a String of letters. The students needed to access each word

in wordList, to correctly call the scrambleWord method of part (a) with the word as the argument,

and to determine whether the word had been changed by scrambling. Upon exiting

scrambleOrRemove, wordList was to contain only words changed by scrambleWord in their

scrambled form. If the word had been scrambled by scrambleWord, the word was replaced in

wordList by the scrambled version of the word. If the word was unchanged by scrambleWord, the

word removed from wordList.

Note: This question involves static methods of a class having no instance variables. The use of

this.scrambleWord or this.anything is incorrect in this question.

Sample: 1A

Score: 8

In part (a) the student correctly accesses all letters in word, looping through all one-letter substrings of

word. The

student correctly identifies all substrings equal to “A” and correctly identifies when the next

substring is not “A”.

The student correctly reverses all pairs of substrings consisting of “A” followed by not “A” by constructing

a new

result string. The student correctly builds the result string, reversing pairs of letters when necessary

and avoids using each “A” in more than one swap by incrementing the loop index an extra time after each

reversal is made. After the loop, the student concatenates the last letter of word to the result string.

However, this is not the correct thing to do in all cases. When the last letter of word is used in a reversal,

it has already been put into the result string and would be duplicated by this assignment. Therefore, the

student does not earn the point for constructing the correct result string. The result string is correctly

returned. The response earned 4 points for part (a).

In part (b) the student correctly accesses all words in wordList using a for-loop. After the remove

meth

od call, the student decrements the index so that no words are skipped.

The student correctly calls the scrambleWord method using a word from wordList as a parameter.

The scrambled word is correctly compared with the original word. If the word is not changed by

scrambleWord, the word is removed from wordList. Otherwise the word is replaced by the result of

scrambling the word. The response earned 4 points in part (b).

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®

COMPUTER SCIENCE A

AP

®

COMPUTER SCIENCE A

2014 SCORING COMMENTARY

Question 1 (continued)

Sample: 1B

Score: 5

In part (a) the student uses a while-loop to access the letters in word. However, the bound on the loop

caus

es the student to fail to access the next-to-last letter of word to check for the last possible pair. The

bound should be word.length – 1. Therefore the point for accessing all letters in is not earned. word

The student correctly reverses all identified pairs of substrings consisting of “A” followed by not “A”. The

letter pair is identified by comparing adjacent one-letter substrings of word. When a pair is found, the

student rebuilds word with the adjacent substrings in reversed order. The student correctly increments

the position in word after a reversal is made so that the “A” is not identified for any more reversals. This

prevents the “A” from bubbling to the end of word. The points for identifying pairs of letters, reversing

the pairs of letters and correctly building the result string are earned. The student fails to return word at

the end of the method, so the point for returning the constructed string is not earned. The response earned

3 points for part (a).

In part (b) the student constructs a new ArrayList, then uses a for-loop to access the words in

wordList.

However, the student uses the remove method inside of the loop without decrementing

the loop control variable, causing a word to be skipped each time remove is called. The point for

accessing all words in wordList is not earned.

The student removes and stores each original word from wordList and correctly calls the

scrambleWord m

ethod to scramble it and store the result. The scrambled word is correctly compared

with the original word. The points for calling the scrambleWord method and for identifying words

changed by scrambling are earned. The student adds each scrambled word to the new ArrayList. At

the end of the method, the student assigns this new ArrayList to wordList. This does not earn the

point for wordList containing the correct words on exit from the method because the parameter is re-

assigned but the original object is not modified. Methods from the List interface must be used to

repopulate wordList with the scrambled words. The response earned 2 points in part (b).

Sample: 1C

Score: 3

In part (a) the student attempts to access the letters in word as if word were a mutable array of

char

acters. Characters are accessed using array indexing and assignments to positions of word are

attempted. A string is an immutable object and letters of the string may not be accessed and manipulated

this way. Therefore, the point for accessing the letters of word is lost. Because the student attempts to

construct a result string by illegally modifying word, the point for reversing a letter pair in the result

string and the point for constructing a correct result string are not earned.

Because of the previous penalties, the comparison of incorrectly accessed letters is allowed in this case. The

logic is correct for identifying at least one pair of letters consisting of “A” followed by a substring that is not

“A” is earned, so this point is earned. The student attempts to do some construction on word for a result

string and then returns the “modified” word. Therefore, the point for returning the constructed result string

is earned. The response earned 2 points for part (a).

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AP

®

COMPUTER SCIENCE A

2014 SCORING COMMENTARY

Question 1 (continued)

In part (b) the point for accessing all words in wordList is not earned because a word would be skipped

afte

r each call to the remove method and the last word in wordList would be skipped in all cases

due to an incorrect loop bound.

The student makes a correct call to the scrambleWord m

ethod using a word from wordList as the

parameter. Even though the student does not assign the returned value of this method call to any variable

so that it can be used, the point for making the correct call is earned. Because the return value of

scrambleWord is not captured, it is not compared to the original word and there is no attempt to replace

the original value by the scrambled version in wordList. The point for identifying words unchanged by

scrambling and the point for wordList containing the correct scrambled words on exit from the method

are not earned. The response earned 1 point in part (b).

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