Solution: Count the Number of Good Subsequences
Understand how to calculate the number of good subsequences in a string using dynamic programming. This lesson covers frequency analysis, binomial coefficient calculations with modular arithmetic, and techniques to avoid counting empty subsequences. Learn to optimize computations with factorials and modular inverses for efficient solving.
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Statement
Count and return the number of good subsequences in the given string s. You may return the modulo
A subsequence is a sequence formed from another sequence by deleting some or no elements while keeping the order of the remaining elements unchanged.
A good subsequence is a subsequence of a string if it is not empty and the frequency of each character is the same.
Constraints:
s.lengthswill only contain ...