1
00:00:00,000 --> 00:00:04,370
OK, so the goal at hand is here, I
have two glasses of colored water.

2
00:00:04,370 --> 00:00:05,730
So we have some purple here.

3
00:00:05,730 --> 00:00:07,220
[WATER POURING]

4
00:00:07,220 --> 00:00:08,710
OK.

5
00:00:08,710 --> 00:00:10,520
And we've got some green here.

6
00:00:10,520 --> 00:00:11,670
[WATER POURING]

7
00:00:11,670 --> 00:00:15,080
And the only goal at hand is
to do a very simple operation

8
00:00:15,080 --> 00:00:16,890
like we needed to do
quite a bit last week,

9
00:00:16,890 --> 00:00:19,710
which is to swap two variables
just like we swap two numbers.

10
00:00:19,710 --> 00:00:22,140
So if you could go ahead and
get the purple liquid in here

11
00:00:22,140 --> 00:00:24,150
and the green liquid in here, go.

12
00:00:27,850 --> 00:00:28,350
[CHUCKLE]

13
00:00:28,350 --> 00:00:29,890
FARRAH: Is it OK if they overlap?

14
00:00:29,890 --> 00:00:31,060
DAVID J. MALAN: Ideally, no.

15
00:00:31,060 --> 00:00:33,570
We want to put only purple
here, and only green here,

16
00:00:33,570 --> 00:00:35,360
and no temporary store.

17
00:00:35,360 --> 00:00:35,860
[LAUGHTER]

18
00:00:35,860 --> 00:00:36,950
FARRAH: Oh.

19
00:00:36,950 --> 00:00:38,700
DAVID J. MALAN: OK,
but you're hesitating.

20
00:00:38,700 --> 00:00:39,900
Why?

21
00:00:39,900 --> 00:00:42,530
FARRAH: Because you told me they
couldn't touch [CHUCKLE] and--

22
00:00:42,530 --> 00:00:44,530
DAVID J. MALAN: Well, you
can touch the glasses.

23
00:00:44,530 --> 00:00:46,260
But you're hesitating to swap them, why?

24
00:00:46,260 --> 00:00:46,920
[CLINK]

25
00:00:46,920 --> 00:00:48,140
OK, that's just cheating.

26
00:00:48,140 --> 00:00:49,600
[LAUGHTER]

27
00:00:49,600 --> 00:00:50,580
[APPLAUSE]

28
00:00:50,580 --> 00:00:53,030
[CHEERS]

29
00:00:53,030 --> 00:00:55,740
OK, very clever.

30
00:00:55,740 --> 00:00:57,870
Supposing you can't
just move things around

31
00:00:57,870 --> 00:01:00,790
in memory, what if I gave
you a temporary variable.

32
00:01:00,790 --> 00:01:01,290
FARRAH: OK.

33
00:01:01,290 --> 00:01:03,210
DAVID J. MALAN: Does this help?

34
00:01:03,210 --> 00:01:05,040
FARRAH: Yes.

35
00:01:05,040 --> 00:01:08,470
DAVID J. MALAN: So how can we now get
purple in there and green in there?

36
00:01:08,470 --> 00:01:09,950
[CHUCKLE]

37
00:01:09,950 --> 00:01:11,990
FARRAH: Can I put purple in here first?

38
00:01:11,990 --> 00:01:12,870
DAVID J. MALAN: Sure.

39
00:01:12,870 --> 00:01:13,620
FARRAH: I'm going to spill it.

40
00:01:13,620 --> 00:01:14,950
DAVID J. MALAN: It's OK.

41
00:01:14,950 --> 00:01:15,950
[WATER POURING]

42
00:01:15,950 --> 00:01:16,990
OK.

43
00:01:16,990 --> 00:01:19,240
So purple goes into the
temporary, very nice.

44
00:01:19,240 --> 00:01:19,740
[APPLAUSE]

45
00:01:19,740 --> 00:01:22,940
FARRAH: Thank you.

46
00:01:22,940 --> 00:01:25,190
DAVID J. MALAN: Green
goes into what was purple.

47
00:01:25,190 --> 00:01:26,310
FARRAH: Yes

48
00:01:26,310 --> 00:01:28,820
DAVID J. MALAN: OK, good.

49
00:01:28,820 --> 00:01:31,550
And then purple goes in--
from the temporary variable

50
00:01:31,550 --> 00:01:34,040
into the original green glass.

51
00:01:34,040 --> 00:01:35,970
Now, a proper round of
applause if we could.

52
00:01:35,970 --> 00:01:36,730
OK.

53
00:01:36,730 --> 00:01:37,230
[APPLAUSE]

54
00:01:37,230 --> 00:01:37,730
Thank you.

55
00:01:37,730 --> 00:01:38,700
FARRAH: Thank you.