## DMPG '15 S6 - Apples to Oranges

View as PDFThey say you cannot compare apples to oranges, but you actually can! In fact, by using money as a medium of exchange, we can compare anything in terms of value. Sun has a single apple. Being the incredibly talented person he is, he's visit a variety of markets with different rates of exchange for his apple. His goal is to obtain infinite apples, and therefore total control of the fruit market.

Suppose the rates of exchange are:

- orange → apples
- apple → oranges

Then it is easy to see that it is in fact impossible to obtain more than one apple through exchanges.

However, if the exchange is:

- orange → apples
- apple → oranges
- apple → grape
- grape → orange

Then Sun can exchange his original apple for a grape, a grape for an orange, and an orange for apples! He can then repeat this to get infinite apples.

The next trivial step is to note that he can now dominate and control the entire apple market.

Your goal is to find out if Sun's fruit market domination scheme is feasible.

#### Input Specification

The first line of input will contain two space-separated integers , the number of different types of fruit, and , the number of exchange rates.

The next lines will each contain the name of a fruit, no longer than alphanumeric characters long. Note that Sun starts with one apple, so `APPLES`

will always be a type of fruit given.

Finally, the last lines will contain an exchange in the space-separated form of , , , indicating that fruit may be exchanged for units of fruit .

#### Output Specification

Output `YA`

on a single line if Sun can get infinite apples, or `NAW`

if he can not.

#### Sample Input

```
3 4
APPLES
ORANGE
GRAPE
ORANGE APPLES 2.0
APPLES ORANGE 0.5
APPLES GRAPE 1.0
GRAPE ORANGE 0.5
```

#### Sample Output

`NAW`

## Comments

Would someone please check the solution which I submit the most recently? I used a BFS that constantly goes backward when the amount of fruits you have right now is greater than the amount of fruit you had before. I don't know what's wrong with it. I kept getting wrong answer.

fruit a may be exchanged for c (0.0<c≤10000.0)(0.0<c≤10000.0) units of fruit b. Does it mean a=cb or b=ca? I'm soooo dumb, never mind, sorry.

unit of fruit can be exchanged for units of fruit , so it's .

Is double accurate enough for this question?

Yes.

Thx

I've been stuck on this problem for a few hours now. Is my idea wrong or is it something else?

Have you considered decimals?

I think so. I've used double to for the decimals. Idk if the decimals would be long enough for some precision errors though.

I checked your code and the problem doesn't seem to be decimals. In fact, some parts of your code seem to be unnecessary. The problem involves performing a BFS (or a similar SSSP algorithm), which means that you don't have to check for the indegree or outdegree. Also, optimize your code a bit and you will AC. (Try using a HashMap)

Decimals are a pain in the asshttps://www.youtube.com/watch?v=hpigjnKl7nI

What exactly is the format of the input? The sample case seems to imply that ".0" will be included in the case that it is an integer. However, experimentation says otherwise.

The exchange rates are decimals

Thanks, I know that they are decimals, the issue seems to be with the format string, in theory, it should work with integers and decimals.

Am I missing something really big here? I have no clue what's wrong......and the fact that there's no output doesn't help it the slightest.

I just ran your submission. It's essentially correct, except that you need to deal with floating point precision when exiting BFS (something like 1e-6 should work).

Thanks so much! Such an easy fix that I would have never found....but now comes the real question....how does a few extra decimal places affect the final result?

Hint: If you're like me, and tried to scan the input as two integers separated by a dot, be aware that the input contains input like "1e-6". And a note to future problem setters, please, if only for my sanity alone, mention it in the problem statement if you have numbers like that. I wasted eight hours today on this one problem.

if I have 0.5 of fruit A, and the exchange rate between fruit A and fruit B is 1:2, does that mean that I can trade 0.5 of fruit A for 1 of fruit B?

Yes

In description, M <= 1000. But there are at least 3 cases M > 1000.

Thanks for noticing: the upper bound for is . I've updated the problem statement.

Can you trade back?

1 Grape = 3 Oranges.

Is this equivalent to:

3 Oranges = 1 Grape?

NAW

No.

is it possible for him to exchange a single apple for half an orange for example?

Yes.