AP COMPUTER SCIENCE A 2016 GENERAL SCORING GUIDELINES

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1 AP COMPUTER SCIENCE A 2016 GENERAL 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., writing t utput, failure t cmpile) 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., 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 cunter example, nte that if the cde declares Bug bug;, then uses Bug.mve() instead f bug.mve(), the cntext des nt allw fr the reader t assume the bject instead f the class The Cllege Bard. Visit the Cllege Bard n the Web:

2 AP COMPUTER SCIENCE A 2016 SCORING GUIDELINES Questin 3: Crsswrd Part (a) tbelabeled 3 pints Intent: Return a blean value indicating whether a crsswrd grid square shuld be labeled with a psitive number +1 Checks blacksquares[r][c] +1 Checks fr black square/brder abve and black square/brder t the left (n bunds errrs) +1 Returns true if square shuld be labeled with psitive number; returns false therwise Part (b) Crsswrd cnstructr 6 pints Intent: Initialize each square in a crsswrd puzzle grid t have a clr (blean) and an integer label +1 puzzle = new Square[blackSquares.length][blackSquares[0].length]; (r equivalent) +1 Accesses all lcatins in puzzle (n bunds errrs) +1 Calls tbelabeled with apprpriate parameters +1 Creates and assigns new Square t lcatin in puzzle +1 Numbers identified squares cnsecutively, in rw-majr rder, starting at 1 +1 On exit: All squares in puzzle have crrect clr and number (minr errrs cvered in previus pints k) Questin-Specific Penalties -2 (p) Cnsistently uses incrrect name instead f puzzle -1 (q) Uses array[].length instead f array[num].length 2016 The Cllege Bard. Visit the Cllege Bard n the Web:

3 AP COMPUTER SCIENCE A 2016 CANONICAL SOLUTIONS Questin 3: Crsswrd Part (a): private blean tbelabeled(int r, int c, blean[][] blacksquares) return (!(blacksquares[r][c]) && (r == 0 c == 0 blacksquares[r - 1][c] blacksquares[r][c - 1])); Part (b): public Crsswrd(blean[][] blacksquares) puzzle = new Square[blackSquares.length][blackSquares[0].length]; int num = 1; fr (int r = 0; r < blacksquares.length; r++) fr (int c = 0; c < blacksquares[0].length; c++) if (blacksquares[r][c]) puzzle[r][c] = new Square(true, 0); else if (tbelabeled(r, c, blacksquares)) puzzle[r][c] = new Square(false, num); num++; else puzzle[r][c] = new Square(false, 0); 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:

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10 AP COMPUTER SCIENCE A 2016 SCORING COMMENTARY Questin 3 Overview This questin used a tw-dimensinal (2-D) array f bjects t represent a crsswrd puzzle. In part (a) students were asked t write a blean methd that determines whether r nt a specific square in the puzzle shuld be numbered based n specified labeling rules. Students needed t demnstrate an understanding f blean data structures, writing and evaluating blean expressins, and returning crrect blean values. Students were als required t demnstrate an understanding f bunds checking and indexing in a 2-D array. This lgic needed t be implemented utilizing given methd parameters. In part (b) students were asked t write a cnstructr that initializes the instance variable and explicitly calls the methd defined in part (a) t build a puzzle, square by square. Students were required t demnstrate an understanding f bject instantiatin by initializing the class instance variable and a Square bject using apprpriate parameter values. Students were required t demnstrate an understanding f 2-D array prcessing by traversing a 2-D array in rw-majr rder, accessing each psitin f the array withut ging ut f bunds. Students were als required t identify squares that needed t be cnsecutively numbered by calling the previusly defined tbelabeled methd using apprpriate parameters. Sample: 3A Scre: 8 In part (a) the student checks the square at rw r, clumn c and crrectly implements the crsswrd labeling rules by checking fr a white square in the first rw r first clumn, r fr a white square with a black square t its left r abve. N checks cause a bunds errr. The lgic crrectly returns true if the square shuld be numbered and false therwise. Part (a) earned 3 pints. In part (b) the student crrectly instantiates the instance variable puzzle with the same dimensins as the parameter blacksquares. All lcatins in puzzle are accessed withut bunds errrs and assigned a Square bject, but the assignment is missing the new peratr, s the "assign new Square" pint was nt earned. Labeled squares, identified by a crrect call t the tbelabeled methd, are numbered cnsecutively in rw-majr rder starting at 1. Squares that are nt labeled are numbered with 0. Part (b) earned 5 pints. Sample: 3B Scre: 5 In part (a) the student fails t check the square at rw r, clumn c, s the first rubric pint was nt earned. The square abve and the square t the left are checked with n bunds errr, s the secnd rubric pint was earned. Because the lgic des nt include checking the clr f the square t be labeled, the third rubric pint was nt earned. Part (a) earned 1 pint. In part (b) the student crrectly instantiates the instance variable puzzle with the same dimensins as the parameter blacksquares. All lcatins in puzzle are accessed withut bunds errrs and assigned a crrectly cnstructed Square bject. The student fails t call the tbelabeled methd, s the "calls tbelabelled" pint was nt earned. Squares are numbered cnsecutively in rw-majr rder starting at 1. Squares that are nt labeled are numbered with 0. Because the squares t be labeled are nt crrectly identified (and because all created squares are black), the final pint was nt earned. Part (b) earned 4 pints The Cllege Bard. Visit the Cllege Bard n the Web:

11 AP COMPUTER SCIENCE A 2016 SCORING COMMENTARY Questin 3 (cntinued) Sample: 3C Scre: 3 In part (a) the student checks the square at rw r, clumn c and crrectly implements the crsswrd labeling rules by checking fr a white square in the first rw r first clumn, r fr a white square with a black square t its left r abve. N checks cause a bunds errr. The lgic used fr the return value is incrrect. In rder t be labeled, inner white squares will require a black square bth abve and t the left, but because nly ne adjacent black square is required, the student did nt earn the third rubric pint. Part (a) earned 2 pints. In part (b) the student incrrectly includes Square[][] t declare a lcal bject rather than instantiating the instance variable, puzzle, s the "initialize puzzle" pint was nt earned. All lcatins in puzzle are accessed withut bunds errrs and assigned a Square bject, but the cnstructr call t Square has an unknwn variable as its first parameter, s the "assign new Square" pint was nt earned. Labeled squares, identified by a call t the tbelabeled methd, are numbered with either 1 r 0, s the "number identified squares" pint was nt earned. The call t the tbelabeled methd uses a blean value as the third parameter rather than a 2-D blean array value, s the "calls tbelabelled" pint was nt earned. Unlabeled white squares are nt numbered with 0, s the final pint was nt earned. Part (b) earned 1 pint The Cllege Bard. Visit the Cllege Bard n the Web: