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  • And this will be a two part exercise as well.

  • And the first goal at hand is for you to choose.

  • Do you want to go first or dad, is it?

  • Would you like your dad to go first?

  • DAVID: OK.

  • I'll go first.

  • DAVID MALAN: You're going to go first.

  • All right.

  • So come on over here.

  • And what I'm going to show David in just a moment is an image on the screen

  • that I'm going to ask that he program you, the audience,

  • to draw giving verbal instructions only.

  • The goal of which is for him to be as precise as possible

  • and as correct as possible to compel the audience, much like a computer,

  • to follow his instructions.

  • And in turn, implement your algorithm.

  • So in just a moment, David is going to rattle off step

  • by step instructions for having everyone in the audience draw this.

  • You are the only one that can see what's on the screen.

  • Everyone in the audience just about has a piece of paper and a pen or pencil.

  • And I just need you very confidently, clearly,

  • to recite step by step instructions by which everyone with their pen or pencil

  • can draw what you see on the screen here.

  • Makes sense?

  • DAVID: Yes.

  • DAVID MALAN: You may use any verbal instructions you like.

  • DAVID: OK.

  • DAVID MALAN: All right.

  • Just about ready to begin?

  • The goal, precision correctness.

  • Begin.

  • DAVID: OK.

  • Step 1.

  • Draw a sideways square.

  • [LAUGHTER]

  • Sideways.

  • 45 degrees rotated.

  • Yeah.

  • DAVID MALAN: OK.

  • DAVID: From the bottom three corners, draw a straight line down

  • that's approximately the length of each side of the square.

  • DAVID MALAN: Unfortunately, programs cannot ask questions of programmer.

  • So we continue on with the next step.

  • DAVID: And finally, between the first and second line,

  • draw a line connecting the two at the end.

  • And between the second and third line, draw a line connecting the end.

  • DAVID MALAN: All right.

  • How do you feel about your instructions?

  • Precise and correct?

  • DAVID: Wishy-washy.

  • DAVID MALAN: Wishy-washy.

  • OK.

  • All right.

  • So let's go ahead.

  • Hang on to the mic for just a moment.

  • I'm going to hop down into the audience with our TFs just

  • to grab a few representative solutions.

  • If you wouldn't mind my grabbing a few sheets of paper

  • from folks who have participated.

  • Let me take a few over here, just a random sample.

  • Welcome to volunteer proactively or keep it to yourself.

  • Let me go in over here.

  • OK.

  • Thank you so much.

  • Any takers over here?

  • OK.

  • All right.

  • Good.

  • Thank you.

  • And all right.

  • The TFs are grabbing a couple too.

  • See some over here.

  • All right.

  • That should do.

  • Let me grab these from Brian over here and Emma.

  • Oh, those are blank.

  • All right.

  • So I think we have plenty over here.

  • So let's take a look before we do part two of two, if I may,

  • at how well David programmed the audience.

  • I'm going to go ahead in just a moment and pull up

  • a projection of some of these drawings here that

  • are the results of these operations.

  • So let me flip through.

  • Get a sample here.

  • And I see a lot of good options here.

  • I see this picture here, which perhaps resembles what you drew.

  • See this one here the top corner, very similar in spirit.

  • This one left a lot of room for other things but--

  • [LAUGHTER]

  • This one was a little more abstract, if I may.

  • [LAUGHTER]

  • And so, let me go over to a spoiler to show you what it

  • is David was programming you to draw.

  • And with some suspense, he was compelling you

  • to draw we hope this here.

  • All right.

  • So close or not close perhaps.

  • All right.

  • Round of applause for David, if we could.

  • [APPLAUSE]

  • DAVID MALAN: Thank you.

  • One moment.

  • And so, you gave pretty--

  • you used, if you would, abstractions in discussing this.

  • You said a sideways square, used 45 degree angles

  • hoping that folks would presumably know what you mean by that.

  • Why did you not just say draw a cube, for instance?

  • DAVID: I thought that would be cheating.

  • DAVID MALAN: OK.

  • Well, it would not have been cheating, but it would

  • have been a wonderful abstraction.

  • If everyone in the room, assuming, knows what in a cube is,

  • you might then be compelled to draw it quite quickly.

  • But that, too, leaves ambiguity and lacks precision.

  • Well, how is the cube oriented?

  • Is it this way?

  • Is it that way?

  • Is a curved this way?

  • So sometimes, these abstractions aren't sufficiently helpful.

  • So I probably would have done what you did as well.

  • Now let's do one other example here, if we could.

  • I'm going to go ahead in just a moment and project an image onto the screen

  • that everyone in the audience can see except you two.

  • Let me go ahead and re angle this a little bit.

  • And if father and son would like to get together or solo draw

  • a picture that the audience is going to tell you how to draw.

  • So we're going to flip the roles now.

  • You all will see the drawing on the screen.

  • We ask that you tell our volunteers what to draw.

  • You can use any words that you want, but you cannot ask questions and no

  • physical gestures to explain.

  • All right.

  • Unfortunately, it's a little hard technologically here

  • in that the solution is going to be there.

  • The solution is going to be there.

  • So we're going to have to put some visors on you, if we could--

  • [LAUGHTER]

  • --so that you can only see straight forward.

  • And if you don't mind hugging the board as close as possible,

  • but occasionally back up so that people can see what you're drawing,

  • but resist the temptation to look up, over left or right.

  • All right.

  • So for our audience then, the images.

  • And if you two could focus only on the board now.

  • Only on the board and definitely not facing that screen.

  • OK.

  • [LAUGHTER]

  • The audience is about to see the picture in question.

  • And so, we need a volunteer first from the audience

  • to call out an instruction.

  • Any step ones?

  • Over here.

  • Make a circle.

  • [LAUGHTER]

  • I heard a small--

  • I heard draw a smaller circle.

  • I didn't hear use the eraser, but OK.

  • OK.

  • No looking at me.

  • All right.

  • So I'll take a third step.

  • So let's go to someone else.

  • Yeah.

  • AUDIENCE: Draw a vertical line.

  • DAVID MALAN: Draw a vertical line.

  • AUDIENCE: From the center of the circle.

  • DAVID MALAN: From the center of the circle.

  • AUDIENCE: From the bottom of the circle and down.

  • DAVID MALAN: From the bottom of the circle and down.

  • AUDIENCE: Large stick figure that appears to be walking.

  • [LAUGHTER]

  • DAVID MALAN: I hear an abstraction.

  • So we were also given a fourth instruction.

  • Draw a stick figure that appears to be walking, if that helps.

  • But I think we're going to need to be more precise here

  • because I can imagine a stick figure doing multiple things in multiple--

  • [LAUGHTER]

  • With--

  • [LAUGHTER]

  • OK.

  • Maybe step five.

  • Do we want to make any tweaks?

  • AUDIENCE: It's an almost upside down triangle.

  • DAVID MALAN: Draw an almost upside down triangle, I heard.

  • AUDIENCE: For the legs.

  • DAVID MALAN: Through the legs.

  • AUDIENCE: For the legs.

  • DAVID MALAN: For the legs.

  • AUDIENCE: After the vertical line coming down.

  • AUDIENCE: You need to erase the legs.

  • DAVID MALAN: OK.

  • I heard erase the legs.

  • AUDIENCE: Get rid of the arms.

  • DAVID MALAN: And get rid of the arms.

  • [LAUGHTER]

  • OK and step five was?

  • AUDIENCE: From the bottom of the vertical line, the body,

  • make the two legs are like a triangle without the bottom.

  • DAVID MALAN: From the bottom of the body,

  • draw like a triangle to represent the legs.

  • AUDIENCE: But not--

  • [LAUGHTER]

  • DAVID MALAN: But not that way.

  • That's good.

  • Let's move on to step six.

  • Step six.

  • Someone over here.

  • AUDIENCE: So once they erase that triangle,

  • from the bottom of the vertical line, draw

  • an upside V, where the center of the V is touching

  • the bottom of that bottom line.

  • DAVID MALAN: From the bottom of the straight line, draw an upside down V.

  • I think we did that.

  • Can you step aside just so the audience can see?

  • Now we have a tripod.

  • OK.

  • [LAUGHTER]

  • OK.

  • So I think we're there.

  • I think we're there.

  • One other instruction.

  • Let's see if we can take this home.

  • Yes, right here.

  • AUDIENCE: Draw a less than symbol, starting from the base of the middle

  • of the circle.

  • DAVID MALAN: Draw a less than symbol from the base

  • of the middle of the end of the circle on the left side.

  • DAVID: Wait, a less than symbol.

  • DAVID MALAN: Less than symbol.

  • Yep.

  • DAVID: Less than.

  • DAVID MALAN: Yes.

  • DAVID: Here?

  • DAVID MALAN: So this is what we call a condition.

  • So, yes.

  • AUDIENCE: Correct.

  • DAVID MALAN: Correct, I hear.

  • OK.

  • I think we're close.

  • Two more steps, maybe.

  • AUDIENCE: To the top of the circle, write the word Hi

  • with a capital H and lowercase I.

  • DAVID MALAN: OK.

  • From the top left of the head, draw the word hi, capital H lowercase I with--

  • I think did you say a line to it?

  • AUDIENCE: Yes, with a line.

  • DAVID MALAN: With a line to it.

  • Yeah.

  • AUDIENCE: [INAUDIBLE]

  • DAVID MALAN: OK.

  • And can you step aside, just so the audience can see?

  • I think we need just one more step.

  • One more step.

  • OK.

  • Back here.

  • AUDIENCE: From the bottom of the circle on the right hand side--

  • DAVID MALAN: From the bottom of the circle on the right hand side--

  • AUDIENCE: --touching the base of the circle and the vertical line going

  • down--

  • DAVID MALAN: --touching the base of the circle and the vertical line going

  • down--

  • AUDIENCE: --make the letter L--

  • DAVID MALAN: --make the letter L--

  • AUDIENCE: --at a 15 degree angle.

  • DAVID MALAN: I heard at a 15 degree angle?

  • Sure.

  • [LAUGHTER]

  • OK.

  • I think-- I think could we have you take several steps back and look up?

  • And round of applause for our volunteers.

  • [APPLAUSE]

And this will be a two part exercise as well.

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B1 中級

CS50 2019-閱讀8-精準 (CS50 2019 - Lecture 8 - Precision)

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    林宜悉 發佈於 2021 年 01 月 14 日
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