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940. Distinct Subsequences II

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Description

Given a string S, count the number of distinct, non-empty subsequences of S .

Since the result may be large, return the answer modulo 10^9 + 7.

 

Example 1:

Input: "abc"

Output: 7

Explanation: The 7 distinct subsequences are "a", "b", "c", "ab", "ac", "bc", and "abc".

Example 2:

Input: "aba"

Output: 6

Explanation: The 6 distinct subsequences are "a", "b", "ab", "ba", "aa" and "aba".

Example 3:

Input: "aaa"

Output: 3

Explanation: The 3 distinct subsequences are "a", "aa" and "aaa".

 

 

Note:

1. S contains only lowercase letters.
2. 1 <= S.length <= 2000

 

 

Solutions

Python3

Java

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