You should rewrirte your beststrings function to accept only the test sequence and a single string, rather than the array and its length. The caller should then call it once for each string in the array.
The actual algorithm for testing the string should then be:
Set count = 0
FOR EACH character c in string A:
FOR EACH character x in string S:
IF c EQUALS x:
ADD 1 TO COUNT // this character exists in the test sequence
BREAK // no need to test the others
END FOR // tested all characters in S
END FOR // tested each character of A
IF count EQUALS A.length(): // every character matched one of S
PRINT A + "is a best string"