[Leetcode] Is Subsequence

Given a string s and a string t, check if s is subsequence of t.

You may assume that there is only lower case English letters in both s and t. t is potentially a very long (length ~= 500,000) string, and s is a short string (<=100).

A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ace" is a subsequence of "abcde" while "aec" is not).

Example 1:
s = "abc", t = "ahbgdc"

Return true.

Example 2:
s = "axc", t = "ahbgdc"

Return false.

Follow up:

If there are lots of incoming S, say S1, S2, ... , Sk where k >= 1B, and you want to check one by one to see if T has its subsequence. In this scenario, how would you change your code?

public class Solution {
    public boolean isSubsequence(String s, String t) {
        return isSubsequence(s, 0, t, 0);
    }
    
    private boolean isSubsequence(String s, int sStart, String t, int tStart) {
        if(sStart == s.length()) {
            return true;
        }
        for(int i = tStart; i < t.length(); i++) {
            if(s.charAt(sStart) == t.charAt(i)) {
                return isSubsequence(s, sStart + 1, t, i + 1);
            }
        }
        return false;
    }
}

follow up: