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
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