WolfDelaymaster | Topcoder Archive

Problem Statement

Wolf Sothe is playing the game Delaymaster. In this game, he can create new words according to the following rules:

For each positive integer n, the string which consists of n copies of 'w', then n copies of 'o', then n copies of 'l', and finally n copies of 'f' is a valid word.
The concatenation of two valid words is a valid word.
Only the words that can be obtained by rules 1 and 2 are valid. There are no other valid words.

Thus, for example:

By rule 1, "wolf", "wwoollff", and "wwwooolllfff" are valid words.
Then, by rule 2, "wolfwwoollff" is a valid word.
By applying rule 2 twice, "wolfwwoollffwolf" is a valid word.
The string "wfol" is not a valid word (order matters).
The string "wwolfolf" is not a valid word (we can only concatenate, not insert one word into another).
The string "wwwoolllfff" is not a valid word (only two 'o's instead of three).

You are given a String str. Return "VALID" if str is a valid word and "INVALID" otherwise. Note that the return value is case-sensitive: you must return the strings "VALID" and "INVALID" in all-uppercase.

Definition

Class:: WolfDelaymaster
Method:: check
Parameters:: String
Returns:: String
Method signature:: String check(String str)
(be sure your method is public)

Constraints

str will contain between 1 and 50 characters, inclusive.
Each character in str will be 'w', 'o', 'l' or 'f'.

Examples

```
"wolf"
```
```
Returns: "VALID"
```
The first valid word from the examples in the problem statement.
```
"wwolfolf"
```
```
Returns: "INVALID"
```
The second invalid word from the examples in the problem statement.

"wolfwwoollffwwwooolllfffwwwwoooollllffff"

Returns: "VALID"

```
"flowolf"
```
```
Returns: "INVALID"
```

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