I can't help with this problem, but I can help you with the statements as I have solved it before. If I remember correctly, you were given a string S consisting of +s and -s, and you are to determine whether the string is valid or not. The following conditions help you determine whether or not a string is valid:

1. An empty string is valid.
2. If S is valid, then +S+ and -S- are valid strings.

For example strings -- and +--+ are valid, where -+ is not.

If the string is valid print YES, otherwise print NO.

Input limits: |S| <= 10^5, where |S| is the length of the string S.

You can use Google Cache to view problem statement: http://webcache.googleusercontent.com/search?q=cache:http://codeforces.net/problemset/problem/343/B