String validation in basic chess model

Question

I get a string which size is 16 (location of chess pieces on the mini-chess-board). This string may contain only symbols:

K (king)
P (pawn)
N(knight)
R(rook)
B(bishop)
Q (queen)
and whitespaces (free field).

How can i validate this string with regex to check if string size is really 16, symbols are only of these and also it should necessarily contain one K symbol (because one King should be)

I tried [KQBNRP ]{16} but now cant check for a K symbol

Thank you

`Q` does not appear in your list of symbols. I guess it means **Queen**. `Q` should also appear only once in the string, no? — Abra, May 31 '20 at 10:43
@Abra yeah, you're right, but different is King must be, Queen may be or may not — Neighbourhood, May 31 '20 at 10:49
it even doesn't matter because i just want to know how to work with regex in this case, when string should be one size and keep a certain symbol for a once. — Neighbourhood, May 31 '20 at 10:50
Use negative lookahead to rule out 2 K's: `(?!.*K.*K)[KQBNRP ]{16}` — Kevin Anderson, May 31 '20 at 10:52

score 1 · Accepted Answer · answered Jun 01 '20 at 11:57

As you know exactly which chars are allowed, you could use a single positive lookahead assertion for a single occurrence of K

Then match any of the listed 16 times using your pattern [KQBNRP ]{16}

^(?=[QBNRP ]*K[QBNRP ]*$)[KQBNRP ]{16}$

Regex demo

Explanation

^ Start of string
(?= Positive lookahead, assert that form the current position what is on the right is
- [QBNRP ]*K[QBNRP ]*$ Match a K between what is in the character class except for the K
) Close the group
[KQBNRP ]{16} Match 16 times any of the listed
$ End of string

String validation in basic chess model

1 Answers1