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[Problem C
| 1994 East-Central Regional problem set
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1994 East-Central Regionals of the ACM International Collegiate Programming Contest
Problem B
Simply Syntax
In the land of Hedonia the official language is Hedonian. A Hedonian
professor had noticed that many of her students still did not master
the syntax of Hedonian well. Tired of correcting the many syntactical
mistakes, she decided to challenge the students and asked them to
write a program that could check the syntactical correctness of any
sentence they wrote. Similar to the nature of Hedonians, the syntax of
Hedonian is also pleasantly simple. Here are the rules:
0. The only characters in the language are the characters
p through z and N,
C, D, E, and
I.
1. Every character from p through z
is a correct sentence.
2. If s is a correct sentence, then so is
Ns.
3. If s and t are correct sentences, then so are
Cst, Dst,
Est, and Ist.
4. Rules 0. to 3. are the only rules to determine the syntactical correctness
of a sentence.
You are asked to write a program that checks if sentences satisfy the syntax
rules given in Rule 0. - Rule 4.
Input
The input consists of a number of sentences consisting only of
characters p through z and
N, C, D,
E, and I. Each sentence is ended by
a new-line character. The collection of sentences is terminated by the
end-of-file character. If necessary, you may assume that each sentence
has at most 256 characters and at least 1 character.
Output
The output consists of the answers YES for each
well-formed sentence and NO for each not-well-formed
sentence. The answers are given in the same order as the
sentences. Each answer is followed by a new-line character, and the
list of answers is followed by an end-of-file character.
Sample Input
Cp
Isz
NIsz
Cqpq
Sample Output
NO
YES
YES
NO
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Ed Karrels.
Last updated September 20, 1999