Practice(easy)
Little Elephant and Balance
A Little Elephant from the Zoo of Lviv likes lucky strings, i.e., the strings that consist only of the lucky digits 4 and 7.
Little Elephant and Strings
A Little Elephant from the Zoo of Lviv likes lucky strings, i.e., the strings that consist only of the lucky digits 4 and 7.
The Little Elephant has K favorite lucky strings A1, A2, ..., AK. He thinks that the lucky string S is good if either |S| ≥ 47 or for some j from 1 to K we have that Aj is a substring of S.
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