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.rabbbitrabbbitrabbbit
Example 2:
Input: s = "babgbag", t = "bag" Output: 5 Explanation: As shown below, there are 5 ways you can generate "bag" from S.babgbagbabgbagbabgbagbabgbagbabgbag
Constraints:
1 <= s.length, t.length <= 1000sandtconsist of English letters.