Hello! This is page 6 of the course called “Y Combinator for Non-programmers”. If you just got here, click here to read from the beginning.

Non-programmers

Slide 1 / 21

This is the final page of the beginner levels. Thank you for following along so far.

Warning: The “Lunchbox” puzzles on this page are much harder than before. But I think you’ll still be able to solve them. Good luck!

The puzzles are hard, but you can do it!

Looking for some other page?

Slide 2 / 21

From now on, you’ll be solving much harder puzzles like this one:

The “Lunchbox” puzzle with 3 rows

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Hmm… previously, we’ve only dealt with lunchboxes with 2 rows.

But this one has 3 rows vertically.

Also, there are 3 items on the bottom row: sushi , a sandwich , and another sushi .

None of the lunchboxes we saw on the last page had 3 items in one row.

Right. Also, did you realize that there are numbers like 1 and 2 on the left edge?

There are numbers like 1 and 2

on the left edge

on the left edge

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That’s true…

How should we solve puzzles like this?

I’ll show you.

- First: I’ll explain how to solve lunchbox puzzles with 3 rows.
- Then: I will give you Yes / No quizzes to solve.

Ok, sounds good.

Slide 3 / 21

The first step in solving a “Lunchbox” puzzle with 3 rows is to focus on the pair of 1’s.

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Focus on the pair of 1’s

More specifically: You need to take a look at the sections that have a 1 on their top-left corner or bottom-left corner.

Let’s see what that means. Press Next :

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The pair of 1’s became pink 1’s.

Also, the top row now has a darker color .

Right. This means:

- Focus on the bottom two rows, which correspond to the pair of 1’s, and
- Ignore the top row for now.

Focus on the bottom two rows, and

Ignore the top row for now

Ignore the top row for now

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Slide 4 / 21

Next: we add the labels. Press Next :

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In addition to t l, and r…

There’s a new label m for the sandwich .

There’s a new label m

for the sandwich

for the sandwich

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tl

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m

r

Yes, this is new: None of t, l, or r apply to the middle item on the bottom row.

In that case, we add the label m (for “Middle”) to it.

m

Add m to the middle item

on the bottom row

on the bottom row

I see. Then what do we do with the m’s?

Slide 5 / 21

Answer: You can ignore m’s for now.

mm

Ignore m’s for now

Why? Take a look at the next steps:

- Match: l r
- Copy: t r
- Remove: t l

None of them involves m. So, while we do these next steps, you can ignore m’s.

Ignore the sandwich labeled as m

for the next several steps

for the next several steps

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tl

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m

r

Got it. Let’s continue then.

Slide 6 / 21

Next: We’ll finish the section that belongs to the pair of 1’s.

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Finish the pair of 1’s

This will be a review of the last page.

First: We check to see if some of l’s and r’s match. If they match, add the sign. Press Next :

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tl

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m

r

Next: We copy t’s to where the matched r’s are.

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tl

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m

r

Finally: We remove t’s and l’s.

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tl

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m

r

See, none of the above steps involved m, right?

I see—that’s why we can ignore m for now.

Slide 7 / 21

Let’s keep going! Press Next :

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tl

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- t and l are removed,
- The pair of 1’s are also removed, and…
- The pair of 2’s became the new pair of 1’s.

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Slide 8 / 21

We now have a simpler lunchbox.

We now have a simpler lunchbox

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1

Yes. Also, notice that:

- The sandwich was labeled as m earlier…
- But it is now labeled as l because it’s on the “Left” now.

The sandwich is now labeled as l

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tl

1

r

Let’s keep going to the end. Press Run :

Press Run . (Or press to step through manually.)

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tl

1

r

We’re left with a hamburger .

That’s it! Were you able to follow?

Hmm… I might need to look at it one more time.

Ok, let’s do a review just in case.

We’ll run it from the beginning to the end using the Run button.

Press Run . (Or press to step through manually.)

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To summarize:

- Start with the pair of 1’s.
- Label the middle item on the bottom row as m, and ignore it.
- After finishing the pair of 1’s, the pair of 2’s becomes 1’s. Then, repeat.

Is this right?

Perfect. Let’s do a Yes / No quiz to check your understanding.

Alright, bring it on!

Slide 9 / 21

Take a look at this lunchbox:

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Question: If we run the above lunchbox, will it eventually become the following?

It’s okay if you have no idea.

Just guess!