CMPSCI 119 Spring 2014 Friday, November 7, 2014 Midterm #2 Solution Key Professor William T. Verts

Transcription

1 CMPSCI 119 Spring 2014 Friday, November 7, 2014 Midterm #2 Solution Key Professor William T. Verts

2 <1> 20 Points Rewrite the following code to use for-loops instead of while-loops. Use as few Python statements as possible without changing how the function works. H = getheight(canvas) W = getwidth(canvas) X = 0 while (X < W): Y = 0 while (Y < H): PX = getpixel(canvas,x,y) setcolor(px,newcolor) Y = Y + 1 X = X + 1 H = getheight(canvas) W = getwidth(canvas) for X in range(w): for Y in range(h): PX = getpixel(canvas,x,y) setcolor(px,newcolor) Expected Answer -or- Expected Answer for X in range(getwidth(canvas)): for Y in range(getheight(canvas)): setcolor(getpixel(canvas,x,y),newcolor) -or- for PX in getpixels(canvas): setcolor(px,newcolor) Acceptable Answer but not: setallpixelstoacolor(canvas,newcolor) Page 1

3 <2> 20 Points What is printed out when Main() is called? def Toad(W,H): print W*3+H def Frog(W,X=5): if (W > X): Toad(X,W) else: Toad(W,W) def Main(): Frog(8) 23 Frog(4,9) 16 In Main: What Frog gets: What Toad gets: What Toad prints: Frog(8) Frog(8,5) Toad(5,8) print 5*3+8 = 23 Frog(4,9) Frog(4,9) Toad(4,4) print 4*3+4 = 16 Page 2

4 <3> 20 Points Variable Mask contains the value [[1,2,3], [4,5,6], [7,8,9]]. Variable Frog contains the value [9, "Cat", (3,8), 4]. What are the results of each of the following statements? If there is any kind of error in the statement, respond with. [4,5,6] X = Mask[1] 7 X = Mask[2][0] 3 X = len(mask) X = Mask[0,0] "a" X = Frog[1][1] (3,8) X = Frog[2] 4 X = Frog[3] 4.0 X = Frog[3]*1.0 X = Frog[3][6] 8 X = Frog[2][1] [4,5,6,9] X = Mask[1]+[Frog[0]] [1,2,3,4,5,6] X = Mask[0]+Mask[1] 4 X = len(frog) 3 X = len(frog[1]) 2 X = len(frog[2]) X = len(frog[3]) "Catfish" X = Frog[1]+"fish" X = Frog[2]+"fish" [9,"Cat",(3,8),4,9,"Cat",(3,8),4] X = Frog+Frog 10 X = Frog[0]+1 Page 3

5 <4> 20 Points We know that pixel-transform functions (B&W, RGB, negate, gray, etc.) and reflection functions (mirror and flip) can be done in-place in one canvas, but filtering functions (emboss, focus, edge-detect, etc.) and 90 rotation functions each require a new canvas for their results. What about a function that rotates an image by 180? Can this be done in-place, or does it require a new canvas? Either explain your answer in words, or write a function that demonstrates your answer. This can be done in-place. The process requires that all pixels be scanned from the upper-left corner to the middle of the canvas, and swapped with their counterparts relative to the lower-right corner. The scan stops after exactly half the pixels in the canvas have been scanned. def Rotate180 (Canvas): H = getheight(canvas) W = getwidth(canvas) P = W * H X1 = 0 Y1 = 0 X2 = W-1 Y2 = H-1 for I in range(p/2): PX1 = getpixel(canvas,x1,y1) PX2 = getpixel(canvas,x2,y2) C1 = getcolor(px1) C2 = getcolor(px2) setcolor(px1,c2) setcolor(px2,c1) X1 = X1 + 1 if (X1 > W-1): X1 = 0 Y1 = Y1 + 1 X2 = X2-1 if (X2 < 0): X2 = W-1 Y2 = Y2-1 Page 4

6 <5> 20 Points A Whoozit is a cyan square of radius 50, with a Thingie centered at each corner. A Thingie is a green square of radius 40, with a Widget in each corner centered 20 pixels from the center of the Thingie. A Widget is a yellow square of radius 15, with a red circle of radius 10 on top, and a white circle of radius 5 on top of that. Fill in the blanks in the functions below to complete the drawing of a Whoozit at location <X,Y>. def addcircle (Canvas, X, Y, R, Fill): addovalfilled(canvas, X-R, Y-R, 2*R+1, 2*R+1, Fill) addoval(canvas, X-R, Y-R, 2*R+1, 2*R+1, black) def addsquare (Canvas, X, Y, R, Fill): addrectfilled(canvas, X-R, Y-R, 2*R+1, 2*R+1, Fill) addrect(canvas, X-R, Y-R, 2*R+1, 2*R+1, black) def addwidget (Canvas, X, Y): addsquare (Canvas, X, Y, 15, yellow) addcircle (Canvas, X, Y, 10, red) addcircle (Canvas, X, Y, 5, white) def addthingie (Canvas, X, Y): addsquare (Canvas, X, Y, 40, green) addwidget (Canvas, X-20, Y-20) addwidget (Canvas, X+20, Y-20) addwidget (Canvas, X-20, Y+20) addwidget (Canvas, X+20, Y+20) def addwhoozit (Canvas, X, Y): addsquare (Canvas, X, Y, 50, cyan) addthingie (Canvas, X-50, Y-50) addthingie (Canvas, X+50, Y-50) addthingie (Canvas, X-50, Y+50) addthingie (Canvas, X+50, Y+50) Page 5