# 0940. Distinct Subsequences II

<https://leetcode.com/problems/distinct-subsequences-ii>

## Description

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.

## ac

```java
```