940. Distinct Subsequences II
Hard
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33

Given a string s, return the number of distinct non-empty subsequences of `s`. Since the answer may be very large, return it modulo `109 + 7`.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., `"ace"` is a subsequence of `"abcde"` while `"aec"` is not.

Example 1:

```Input: s = "abc"
Output: 7
Explanation: The 7 distinct subsequences are "a", "b", "c", "ab", "ac", "bc", and "abc".
```

Example 2:

```Input: s = "aba"
Output: 6
Explanation: The 6 distinct subsequences are "a", "b", "ab", "aa", "ba", and "aba".
```

Example 3:

```Input: s = "aaa"
Output: 3
Explanation: The 3 distinct subsequences are "a", "aa" and "aaa".
```

Constraints:

• `1 <= s.length <= 2000`
• `s` consists of lowercase English letters.
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