public class Solution
extends Object
115 - Distinct Subsequences\.
Hard
Given two strings `s` and `t`, return _the number of distinct subsequences of `s` which equals `t`_.
A string's **subsequence** is a new string formed from the original string by deleting some (can be none) of the characters without disturbing the remaining characters' relative positions. (i.e., `"ACE"` is a subsequence of `"ABCDE"` while `"AEC"` is not).
It is guaranteed the answer fits on a 32-bit signed integer.
**Example 1:**
**Input:** s = "rabbbit", t = "rabbit"
**Output:** 3
**Explanation:** As shown below, there are 3 ways you can generate "rabbit" from S. ` **rabb**b**it**` ` **ra**b**bbit**` ` **rab**b**bit**`
**Example 2:**
**Input:** s = "babgbag", t = "bag"
**Output:** 5
**Explanation:** As shown below, there are 5 ways you can generate "bag" from S. ` **ba**b**g**bag` ` **ba**bgba**g**` ` **b**abgb**ag**` `ba**b**gb**ag**` `babg**bag**`
**Constraints:**
* `1 <= s.length, t.length <= 1000`
* `s` and `t` consist of English letters.