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 <= 1000 <= t.length <= 104sandtconsist 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?