text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
|---|---|---|
quit, even if the list is super-small. | 3,822.041 | 2.399 |
But then, the magic is hidden
in those last three lines. | 3,824.44 | 2.84 |
Else, sort the left
half of the elements, | 3,827.28 | 2.93 |
then sort the right
half of the elements, | 3,830.21 | 1.76 |
which is completely punting so to speak. | 3,831.97 | 2.13 |
Just kind of recursively
calling yourself. | 3,834.1 | 2.04 |
But the key detail here is that then
you have to merge the sorted halves. | 3,836.14 | 4.72 |
You're not just looking for Mike to the
left and looking for Mike to the right. | 3,840.86 | 3.312 |
You're doing something on the
left, something on the right, | 3,844.172 | 2.458 |
sorting each half, but then you have
to kind of weave things together. | 3,846.63 | 3.43 |
And we'll see how
expensive that actually is. | 3,850.06 | 2.85 |
So let's take an example. | 3,852.91 | 1.3 |
And I mocked this up with some
very simple animation so we | 3,854.21 | 3.82 |
could walk through it step-by-step. | 3,858.03 | 1.585 |
But consider the following. | 3,859.615 | 1.125 |
So here is that same
list from before where | 3,860.74 | 1.791 |
we had a whole bunch of volunteers. | 3,862.531 | 1.699 |
But rather than call up humans,
we'll just do this visually. | 3,864.23 | 2.58 |
Let me consider the fact that
this is really just an array. | 3,866.81 | 3.245 |
So I'm just going to box
everything like this. | 3,870.055 | 2.015 |
And this is actually key that we
have random access to these elements. | 3,872.07 | 3.28 |
We can jump right to
the elements we want | 3,875.35 | 1.82 |
and code ultimately, too, if we cared. | 3,877.17 | 2.16 |
And now, let's focus
on the left-hand side. | 3,879.33 | 2.35 |
So I've wrapped 4, 8,
6, 2 in a solid line | 3,881.68 | 4.682 |
and left everything else
dash because I want to focus | 3,886.362 | 2.208 |
our attention on sorting the left half. | 3,888.57 | 2.23 |
So again, to rewind
this is the algorithm. | 3,890.8 | 2.51 |
And the goal at hand is
to walk through visually | 3,893.31 | 2 |
an example whereby we sort 8 elements. | 3,895.31 | 2.684 |
And we do that by sorting the
left half, sorting the right half, | 3,897.994 | 2.666 |
and then somehow merging
these things together. | 3,900.66 | 3.16 |
So how do we do this? | 3,903.82 | 1.14 |
Well, let's consider the left half. | 3,904.96 | 2.23 |
All right. | 3,907.19 | 0.95 |
How do I sort a list of 4 elements? | 3,908.14 | 2.07 |
What does it mean to sort the left half? | 3,910.21 | 1.78 |
Well, what algorithms do I have in
my toolkit for sorting elements? | 3,911.99 | 2.9 |
Yeah, selection sort, insertion
sort, bubble sort, but-- merge sort. | 3,917.64 | 4.68 |
And that's where this
gets weird quickly. | 3,922.32 | 2.29 |
You want to use your same algorithm to
sort the left-hand side of this list. | 3,924.61 | 4.324 |
And yet, we haven't even
finished defining this algorithm, | 3,928.934 | 2.416 |
but that's going to be OK we'll see. | 3,931.35 | 2.13 |
So let's sort the left half. | 3,933.48 | 1.19 |
How do you sort the left half of a list? | 3,934.67 | 1.666 |
Well, you sort a list of size 4. | 3,936.336 | 1.494 |
What does that mean? | 3,937.83 | 0.85 |
How do you sort a list of size 4? | 3,938.68 | 2.66 |
Sort the left half of that. | 3,941.34 | 2.19 |
So let's focus on 4 and 8. | 3,943.53 | 2.19 |
How do you sort a list of size 2? | 3,945.72 | 1.96 |
Merge sort it. | 3,947.68 | 1.25 |
So how do you sort a list of size 2? | 3,948.93 | 1.98 |
Sort the left half. | 3,950.91 | 1.86 |
OK, beautifully. | 3,952.77 | 1.16 |
Done. | 3,953.93 | 1.72 |
Done. | 3,955.65 | 1.29 |
Sort the right half. | 3,956.94 | 1.51 |
Nice, done. | 3,958.45 | 1.56 |
I mean, I'm doing real
work, or claiming to. | 3,960.01 | 2.57 |
But now I have to do something more. | 3,962.58 | 1.69 |
Now I have to merge the two halves. | 3,964.27 | 1.46 |
So I'm taking a step back. | 3,965.73 | 1.33 |
I have two lists now, one
of size 1, one of size 1. | 3,967.06 | 3.579 |
I have to merge these
things, two together. | 3,970.639 | 1.791 |
Which comes first, 4 or 8? | 3,972.43 | 2.69 |
4. | 3,975.12 | 0.67 |
So let's create some extra space for it. | 3,975.79 | 2.03 |
Let's put 4 here and let's put 8 here. | 3,977.82 | 3.53 |
So here's a key detail
with merge sort, kind | 3,981.35 | 2.394 |
of cheating, at least at the
moment, I'm using some extra space. | 3,983.744 | 2.666 |
So I hope you won't mind. | 3,986.41 | 1.23 |
To achieve this, I'm using
more memory, more RAM, | 3,987.64 | 2.76 |
that I wasn't allowing myself
for selection sort, bubble | 3,990.4 | 2.53 |
sort, or insertion sort. | 3,992.93 | 1.011 |
OK. | 3,993.941 | 0.499 |
So now it's going to be
easy to get lost quickly. | 3,994.44 | 2.041 |
So what have I just done? | 3,996.481 | 1.239 |
I have sorted a list of size 2
by sorting the left half, done. | 3,997.72 | 4.06 |
Right half, done. | 4,001.78 | 1.27 |
Merging it together. | 4,003.05 | 1.4 |
So now I have a sorted list of size 2. | 4,004.45 | 3.69 |
Rewind the story. | 4,008.14 | 0.87 |
What step comes next? | 4,009.01 | 2.76 |
Sort the right half. | 4,011.77 | 2.06 |
That was of size 2. | 4,013.83 | 1.2 |
So if you kind of mentally buffer
all of the to-dos that we're doing, | 4,015.03 | 3.5 |
and then pluck them off as we go,
you'll see where the story goes. | 4,018.53 | 3.68 |
Now I want to sort the right
half of the original list. | 4,022.21 | 2.31 |
Sorry, the right half of the
left half of the original list. | 4,024.52 | 4.32 |
How do I do that? | 4,028.84 | 0.94 |
Sort of left half, done. | 4,029.78 | 1.7 |
Sort the right half, done. | 4,031.48 | 1.77 |
Merge them together. | 4,033.25 | 1.21 |
What comes first, 6 or 2? | 4,034.46 | 1.86 |
OK. | 4,036.32 | 0.5 |
So let's give ourselves a
little more memory for that | 4,036.82 | 1.76 |
so we have a place to put it. | 4,038.58 | 1.33 |
2. | 4,039.91 | 0.97 |
And then 6. | 4,040.88 | 1.271 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.