Is Subsequence

Given two strings `s` and `t`, return `true`_ if _`s`_ is a **subsequence** of _`t`_, or _`false`_ otherwise_. 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", t = "ahbgdc" **Output:** true ``` **Example 2:** **Input:** s = "axc", t = "ahbgdc" **Output:** false ```   **Constraints:** - `0 <= s.length <= 100` - `0 <= t.length <= 104` - `s` and `t` consist only of lowercase English letters.   **Follow up:** Suppose there are lots of incoming `s`, say `s1, s2, ..., sk` where `k >= 109`, and you want to check one by one to see if `t` has its subsequence. In this scenario, how would you change your code?