AP Computer Science A

Size: px

Start display at page:

Download "AP Computer Science A"

Kristopher Farmer
5 years ago
Views:

1 2018 AP Cmputer Science A Sample Student Respnses and Scring Cmmentary Inside: Free Respnse Questin 1 RR Scring Guideline RR Student Samples RR Scring Cmmentary 2018 The Cllege Bard. Cllege Bard, Advanced Placement Prgram, AP, AP Central, and the acrn lg are registered trademarks f the Cllege Bard. Visit the Cllege Bard n the Web: AP Central is the fficial nline hme fr the AP Prgram: apcentral.cllegebard.rg

2 AP COMPUTER SCIENCE A 2018 SCORING GUIDELINES Apply the questin assessment rubric first, which always takes precedence. Penalty pints can nly be deducted in a part f the questin that has earned credit via the questin rubric. N part f a questin (a, b, c) may have a negative pint ttal. A given penalty can be assessed nly nce fr a questin, even if it ccurs multiple times r in multiple parts f that questin. A maximum f 3 penalty pints may be assessed per questin. 1-Pint Penalty v) Array/cllectin access cnfusin ([] get) w) Extraneus cde that causes side-effect (e.g., printing t utput, incrrect precnditin check) x) Lcal variables used but nne declared y) Destructin f persistent data (e.g., changing value referenced by parameter) z) Vid methd r cnstructr that returns a value N Penalty Extraneus cde with n side-effect (e.g., valid precnditin check, n-p) Spelling/case discrepancies where there is n ambiguity* Lcal variable nt declared prvided ther variables are declared in sme part private r public qualifier n a lcal variable Missing public qualifier n class r cnstructr header Keywrd used as an identifier Cmmn mathematical symbls used fr peratrs ( < > <> ) [] vs. () vs. <> = instead f == and vice versa length/size cnfusin fr array, String, List, r ArrayList; with r withut ( ) Extraneus [] when referencing entire array [i,j] instead f [i][j] Extraneus size in array declaratin, e.g., int[size] nums = new int[size]; Missing ; where structure clearly cnveys intent Missing where indentatin clearly cnveys intent Missing ( ) n parameter-less methd r cnstructr invcatins Missing ( ) arund if r while cnditins *Spelling and case discrepancies fr identifiers fall under the N Penalty categry nly if the crrectin can be unambiguusly inferred frm cntext, fr example, ArayList instead f ArrayList. As a cunterexample, nte that if the cde declares int G=99, g=0;, then uses while (G < 10) instead f while (g < 10), the cntext des nt allw fr the reader t assume the use f the lwer case variable The Cllege Bard. Visit the Cllege Bard n the Web:

3 AP COMPUTER SCIENCE A 2018 SCORING GUIDELINES Questin 1: Frg Simulatin Part (a) simulate 5 pints Intent: Simulate the distance traveled by a hpping frg Calls hpdistance and uses returned distance t adjust (r represent) the frg s psitin Initializes and accumulates the frg s psitin at mst maxhps times (must be in cntext f a lp) Determines if a distance representing multiple hps is at least galdistance Determines if a distance representing multiple hps is less than starting psitin Returns true if gal ever reached, false if gal never reached r psitin ever less than starting psitin Part (b) runsimulatins 4 pints Intent: Determine the prprtin f successful frg hpping simulatins Calls simulate the specified number f times (n bunds errrs) Initializes and accumulates a cunt f true results Calculates prprtin f successful simulatins using duble arithmetic Returns calculated value 2018 The Cllege Bard. Visit the Cllege Bard n the Web:

4 AP COMPUTER SCIENCE A 2018 SCORING GUIDELINES Questin 1: Scring Ntes Part (a) simulate 5 pints Pints Rubric Criteria Respnses earn the pint if they... Respnses will nt earn the pint if they... Calls hpdistance and uses returned distance t adjust (r represent) the frg s psitin Initializes and accumulates the frg s psitin at mst maxhps times (must be in cntext f a lp) Determines if a distance representing multiple hps is at least galdistance Determines if a distance representing multiple hps is less than starting psitin Returns true if gal ever reached, false if gal never reached r psitin ever less than starting psitin Part (b) runsimulatins use hpdistance() as a psitin, like hpdistance() < 0 use sme number f hps * hpdistance() as the frg s final psitin have checks fr all three cnditins and crrect return lgic based n thse checks, even if a check did nt earn a pint nly use hpdistance() as a cunt, like hpdistance() < maxhps d nt use a lp d nt check all three cnditins nly check fr galdistance after the lp nly check fr starting psitin after the lp 4 pints Pints Rubric Criteria Respnses earn the pint if they... Respnses will nt earn the pint if they... Calls simulate the specified number f times (n bunds errrs) Initializes and accumulates a cunt f true results Calculates prprtin f successful simulatins using duble arithmetic Returns calculated value d nt use the result f calling simulate perfrm the crrect calculatin n an accumulated value, even if there was an errr in the accumulatin d nt use a lp initialize the cunt inside a lp d nt use a lp fail t divide by the parameter calculate values using nnnumeric types return a cunt f simulatins 2018 The Cllege Bard. Visit the Cllege Bard n the Web:

5 AP COMPUTER SCIENCE A 2018 SCORING GUIDELINES Questin 1: Frg Simulatin Part (a) public blean simulate() int psitin = 0; fr (int cunt = 0; cunt < maxhps; cunt++) psitin += hpdistance(); if (psitin >= galdistance) return true; else if (psitin < 0) return false; return false; Part (b) public duble runsimulatins(int num) int cuntsuccess = 0; fr (int cunt = 0; cunt < num; cunt++) if(simulate()) cuntsuccess++; return (duble)cuntsuccess / num; These cannical slutins serve an expsitry rle, depicting general appraches t slutin. Each reflects nly ne instance frm the infinite set f valid slutins. The slutins are presented in a cding style chsen t enhance readability and facilitate understanding The Cllege Bard. Visit the Cllege Bard n the Web:

6 e e =,: :: ::: n e p ria :: ::: : pa::: y t C m:: *,r ::::re: :::: m:::r Returns true if the frg successfully reached r passed the gal during the simulatin; * false therwise. */ public blean simulate(), n tvi.rre,n+. l" -t """' i:- O;-., 7 recffive full 0. ir (i,j i ""0, I < rn.x \ p!'>; it+) 1 (,1,.((e,, J I) i& ""U +:: h p \);s\-m0t,(), 1 S ( u,rre. JD;s ""u (. Q) f 1 re,\,..._rv'\ t.lse., I 1 ( c,,,_rṛw-i l),.) 'll'ic.t,t\.i (">'\ +(1-.e, I > j"'\ D..., "(,... ) 1 Part (b) begins n page 8 Unauthrized cpying r reuse f any part f this page Is Illegal.. 7. GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

7 (b) Write the runsimulatins methd, which per f rms a given number f simulatins and returns the / J1 I prprtin f simulatins in which the frg successfully reached r passed the gal. Fr example, if the ; / paramcter passedl runsimulatins is 400, and100fthe400 simulate methd calls retumed true, then the runsimulatins methd shuld return. 25. Cmplete methd runsimulatins belw. Assume that simulate wrks as specified, regardless f what yu wrte in part (a). Yu must use simulate apprpriately t receive full credit. I** Runs num simulatins and returns the prprtin f simulatins in which the frg * successfully reached r passed the gal. * Precnditin: num > 0 */ public duble runsimulatins(int num) t '" \ ""'ti\.sl,\(<,t \ -:. 0 i ( (,,l i -:. 0; i c: I"\ l<t,"1; i H) \ \\ ( Silh \.\.t. ()) ) 1 J rel,..._ ( (J\\blt) ()w'1' st-\cw s) / (IV.t'"n Unauthrized cpying r reuse f any part f this pag Is Illegal. -8- GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

8 Cmplete methd simulate belw. Yu must use hpdistance apprpriately t,receive full credit. I* * Simulates a frg attempting t reach the gal s described in part (a). / tl * Returns true if the frg successfully reached r passed the gal during the simulatin; * false therwise. */ public blean simulate() L \ \ t 6,s-\- = 0, \\\- ct\ J \J\s-\eil\le,) f,or..\ \ =-0 \\ <-::. 11\X c;'.) \HJ b, s-\- t 01r t)\s tg\f\ ce(.)), t le\, -\.! ) '[ e\se, re-¾t.trl"\ t, e) r fe,-\-v., (\ 'fc,,j se j 3 Part (b) begins n page 8 Unauthrized cpying r reuse f any part f this page Is Illegal. -7- GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

9 (b) Write the i;:uns; rnulatins methd, which perfrms a given number tsimulatins and r urs.the -erprtjn af simulati.am_in which lhe frg s cce ffi!lly reached r passed the gal. Fr example, if the parameter passed t runsimulatins is. 4, and!qqj>f the 1.Q9_ si late methd calls returned true, then the runchm,,,,,..,,.._..., methd shuld return Cmplete methd runsimulatins belw. Assume that simulate wrks as specified, regardless f what yu wrte i.,12arl (a). Yu must use simulate apprpriately t receive full credit. /** Runs num simulatins and returns the prprtin f simulatins in which the frg * successfully reached r passed the gal. * Precnditin: num > *I public duble runsimulatins ( int num)' l 10-t (Ou(\-\ =\\u.l)'\ \ \\\- fd. c; :: 0 j J0u\,\e t.fi :::... fc( L, l\t i.:: J' nvi1' it f), c 1mv.\ 1cc ') t Unauthrized cpying r reuse at any part at this page la Illegal. -8- GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

10 Cmplete methd simulate belw. Yu must use hpdistance apprpriately t receive full credit. I 'l,a I** Simulates a frg attempting t reach the gal as described in part (a). * Returns true if the frg successfully reached r passed the gal during the simulatin; * false therwise. */ public blean simulate() Part (b) begins n page 8 Unauthrized cpying r reuse f any part f this page Is Illegal. -7- GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

11 (b) Write U1e runsimulatins methd, which perfrms a given number f simulatins and returns the II/ prprtin f simulatins in which the frg successfully reached r passed the gal. Fr example, if the fc' parameter passed t runsimulatins is 400, and 100 f the 400 simulate methd calls returned true, then the runsimulatins methd shuld return O. 25. Cmplete methd runsimulatins belw. Assume that simulate wrks as specified, regardless f what yu wrte in part (a). Yu must use simulate apprpriately t receive full credit. I** Runs num simulatins and returns the prprtin f simulatins in which the frg * successfully reached r passed the gal. * Precnditin: num > 0 */ public duble runsimulatins(int num).t L,\..-Q 'f (\g (,0 "'"'' _, / tr( k=o; < \V-- kt+)f 1f GrfV\"'"ft!JtQ k) = tr t) ', t re t..r/\ (, O v-ṛj f-t; I Unauthrized cpying r reuse f any part f this pag Is lllgal. -8- GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

12 AP COMPUTER SCIENCE A 2018 SCORING COMMENTARY Questin 1 Overview This questin tested the student's ability t: Write prgram cde t create bjects f a class and call methds; and Write prgram cde t satisfy methds using expressins, cnditinal statements, and iterative statements. Students were prvided with the specificatins f the FrgSimulatin class. The FrgSimulatin class encapsulates a simulatin f a frg hpping in a straight line. It cntains tw private integer instance variables, galdistance and maxhps, which represent the distance in inches frm the starting pint t the gal and the maximum number f hps allwed t reach the gal. It als cntains a private methd, hpdistance, which returns an integer representing the distance in inches t be mved when the frg hps. Implementatin fr this methd was nt shwn. In part (a) students were asked t write the FrgSimulatin methd simulate, which determines whether a frg is successful in reaching galdistance. Students were required t use the private methd hpdistance within the cntext f a lp t update an initialized variable representing the frg's psitin. The lp iterates until ne f the fllwing cnditins becmes true: The frg has reached r passed the gal, in which case a value f true is immediately returned. The frg has reached a negative psitin, in which case a value f false is immediately returned. A frg has taken maxhps hps withut reaching the gal, in which case a value f false is returned. In part (b) students were asked t write the FrgSimulatin methd runsimulatins(int num), which uses a lp t call the simulate methd num times. Each time simulate returns true, a previusly initialized variable is incremented. The methd returns a decimal value representing the prprtin f simulatins in which the frg successfully reached r passed the gal. Sample: 1A Scre: 9 In part (a) the respnse earned pint 1 by adjusting a variable representing the frg s psitin with the result f a crrect call t hpdistance. The variable is prperly initialized and is updated within a lp that iterates n mre than maxhps times. Therefre, the respnse earned pint 2. The respnse uses cnditinal statements t crrectly determine if the frg s psitin is greater than r equal t galdistance r if the frg s psitin is less than the starting psitin. Fr this reasn, the respnse earned bth pints 3 and 4. All f the cnditinal statements exist within the cntext f the lp. This allws the respnse t crrectly return true if the gal is met and false therwise. As a result the respnse earned pint 5. Part (a) earned 5 pints. In part (b) pint 6 is earned because the respnse implements a lp t crrectly call simulate exactly num times. A prperly initialized variable is used t accumulate a cunt f true results, s the respnse earned pint 7. The variable is crrectly cast t a duble value prir t being divided by the parameter. Fr this reasn the respnse earned pint 8. The calculated value is returned, and the respnse earned pint 9. Part (b) earned 4 pints The Cllege Bard. Visit the Cllege Bard n the Web:

13 AP COMPUTER SCIENCE A 2018 SCORING COMMENTARY Questin 1 (cntinued) Sample: 1B Scre: 5 In part (a) hpdistance is called crrectly, and the returned result is used t adjust a variable representing the frg s psitin. An imprperly structured assignment peratr is used. Hwever, this is a nnpenalized errr, and the respnse earned pint 1. Because an incrrect lp terminating cnditin allws fr the frg s psitin t be updated mre than maxhps times, the respnse did nt earn pint 2. Pint 3 was earned when a cnditinal was used t determine if the frg s psitin has reached r exceeded galdistance. Because the respnse des nt include a check t determine if the frg s psitin is less than the starting psitin, the respnse did nt earn pint 4. Fr multiple reasns, the lgic f the return statement is incrrect. First, the galdistance check ccurs utside f the lp, s the respnse culd return an incrrect result after the gal has been reached. Secnd, there is n determinatin as t whether the distance is less than the starting psitin. As a result the respnse culd return an incrrect result after a negative psitin has been achieved. Fr either f these reasns, the respnse did nt earn pint 5. Part (a) earned 2 pints. In part (b) simulate is called mre than num times due t an incrrect terminating cnditin within the lp. Therefre, the respnse did nt earn pint 6. Pint 7 was earned because a variable is initialized and crrectly used t cunt true results. The variable is crrectly cast as a duble and is divided by a variable cntaining the parameter value, s the respnse earned pint 8. The calculated value is returned, and the respnse earned pint 9. Part (b) earned 3 pints. Sample: 1C Scre: 3 In part (a) hpdistance is called, and the returned result is used t adjust a variable representing distance. Because hpdistance is a parameter-less methd, the missing parenthesis is a nnpenalized errr. Therefre, the respnse earned pint 1. Fr several reasns, the respnse des nt include the required elements t earn pint 2. First, the terminating cnditin f the lp des nt refer t maxhps but instead refers t a variable that is neither declared nr initialized. Secnd, the cmparisn peratr within the terminating cnditin f the lp allws hpdistance t be called mre than maxhps times. Finally, the variable used t adjust distance is neither declared nr initialized. Fr any f these reasns, the respnse did nt earn pint 2. Because the respnse des nt refer t galdistance in the attempt t determine if the frg reached the gal, the respnse did nt earn pint 3. The respnse des nt include a check t determine if the frg s psitin is less than the starting psitin, s the respnse did nt earn pint 4. Because the starting psitin check is mitted, the respnse will nt always return a crrect value. Therefre, the respnse did nt earn pint 5. Part (a) earned 1 pint. In part (b) the respnse did nt earn pint 6 because simulate is called incrrectly by including a parameter in the methd call. A prperly initialized variable is used t accumulate a cunt f true values, s the respnse earned pint 7. The calculatin f the prprtin f successful simulatins is incrrectly cast as a duble, s the respnse did nt earn pint 8. The calculated result is returned. Therefre, the respnse earned pint 9. Part (b) earned 2 pints The Cllege Bard. Visit the Cllege Bard n the Web:

AP Computer Science A

AP Computer Science A 2018 AP Cmputer Science A Sample Student Respnses and Scring Cmmentary Inside: Free Respnse Questin 3 RR Scring Guideline RR Student Samples RR Scring Cmmentary 2018 The Cllege Bard. Cllege Bard, Advanced