Problem: Count the Number of Good Subsequences

Medium

30 min

Explore how to count good subsequences in a string using dynamic programming. Understand the problem constraints and implement solutions that handle character frequency requirements. This lesson helps you develop skills to solve optimization problems with subsequences, returning counts modulo a large prime to manage large outputs.

Statement

Count and return the number of good subsequences in the given string s. You may return the modulo $10^9 + 7$ of the count.

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:

$1 \leq$ s.length $\leq 10^4$
s will only contain lowercase English characters.

Problem: Count the Number of Good Subsequences

Medium

30 min

Statement

Count and return the number of good subsequences in the given string s. You may return the modulo $10^9 + 7$ of the count.

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:

$1 \leq$ s.length $\leq 10^4$
s will only contain lowercase English characters.

Problem: Count the Number of Good Subsequences

Statement

Examples

Understand the problem

Figure it out!

Try it yourself

Problem: Count the Number of Good Subsequences

Statement

Examples

Understand the problem

Figure it out!

Try it yourself