unique-substrings-with-equal-digit-frequency

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2168. Unique Substrings With Equal Digit Frequency (Medium)

Related Topics

[Hash Table] [String] [Counting] [Hash Function] [Rolling Hash]

Hints

Hint 1

With the constraints, could we try every substring?

Hint 2

Yes, checking every substring has runtime O(n^2), which will pass.

Hint 3

How can we make sure we only count unique substrings?

Hint 4

Use a set to store previously counted substrings. Hashing a string s of length m takes O(m) time. Is there a fast way to compute the hash of s if we know the hash of s[0..m - 2]?

Hint 5

Use a rolling hash.