Sequence Check

Prereq: Knapsack Intro

Given 2 strings determine how many distinct subsequences of s equal t. A subsequence of s is a the original sequence s with some characters deleted. The answer is guaranteed to be less than 2^31-1.


1 <= s.length, t.length <= 100001

The strings s and t will only contain lowercase english letters


Example 1

Input: s = "rabbbit", t = "rabbit"
Output: 3

You can remove any of the 3 middle b values from s to make the t value

Try it Yourself



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1  >>> a = [1, 2, 3]
2  >>> a[-1]
3  3

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