[LC] 392. 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?

class Solution {
    public boolean isSubsequence(String s, String t) {
        if (s == null || s.length() == 0) {
            return true;
        }
        int index = 0;
        for (char ch : t.toCharArray()) {
            if (index < s.length() && s.charAt(index) == ch) {
                index += 1;
            }
        }
        return index == s.length();
    }
}